Sin and Cos formulas are given in this article. You can find basic trigonometry formulas, identities, triple angle and double angle formulas. Learn more trigonometry formulas at BYJU'S. Nov 15, 2016 · In Δ ABC the value of cos B is . What is the trigonometric ratio? Trigonometric ratios can be calculated by taking the ratio of any two sides of the right-angled triangle. The basic Trigonometric ratios are : sin θ = cos θ = tan θ = sec θ = cosec θ = cot θ = According to the question . In Δ ABC , Perpendicular for ∠B = 5 . Base for ... Case of acute angle γ, where a < 2b cos γ. Drop the perpendicular from A onto a = BC, creating a line segment of length b cos γ. Duplicate the right triangle to form the isosceles triangle ACP. Construct the circle with center A and radius b, and a chord through B perpendicular to c = AB, half of which is h = BH. Apply the Pythagorean ...tan（-α）= -tanα cot（-α）= -cotα 公式四： 利用公式二和公式三可以得到π-α与α的三角函数值之间的关系： Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more. tan（-α）= -tanα cot（-α）= -cotα 公式四： 利用公式二和公式三可以得到π-α与α的三角函数值之间的关系：Jul 2, 2020 · Therefore, \(\cos(a + b) = \cos(a) \cos(b) – \sin(a) \sin(b)\) Proved. Cos (A+B) Verification. Need to verify cos(a+b)formula is right or wrong. put the value of a =45° degree and b=30° degree. put the value of a and b in the LHS. cos(a+b) = cos(45°+30°) = cos(75°) = \(\frac{√3 – 1}{2√2}\) put the value of a and b in the RHS 38K Followers, 1,078 Following, 3,190 Posts - See Instagram photos and videos from Cos Bar (@cosbar)Voiceover: In the last video we proved the angle addition formula for sine. You could imagine in this video I would like to prove the angle addition for cosine, or in particular, that the cosine of X plus Y, of X plus Y, is equal to the cosine of X. Cosine of X, cosine of Y, cosine of Y minus, so if we have a plus here we're going to have a ...Expert Maths Tutoring in the UK - Boost Your Scores with Cuemath. Tan (a - b) is one of the important trigonometric identities, also known as the tangent subtraction formula, used in trigonometry to find the value of the tangent trigonometric function for the difference of angles. We can find the expansion of tan (a - b) to represent the tan of ...Pythagoras Theorem: (only for Right-Angled Triangles) a2 + b2 = c2. Law of Cosines: (for all triangles) a2 + b2 − 2ab cos (C) = c2. So, to remember it: think " abc ": a2 + b2 = c2, then a 2 nd " abc ": 2ab cos (C), and put them together: a2 + b2 − 2ab cos (C) = c2.Cos a Cos b is the trigonometry identity for two different whose sum and difference are known. It is applied when either the two angles a and b are known or when the and difference of angles are known. It can be derived using cos (a + b) and cos (a - b) trigonometry identities which are some of the important trigonometric identities. Answer: c = 6.67 How to Remember How can you remember the formula? Well, it helps to know it's the Pythagoras Theorem with something extra so it works for all triangles: Pythagoras Theorem: (only for Right-Angled Triangles) a2 + b2 = c2 Law of Cosines: (for all triangles) a2 + b2 − 2ab cos (C) = c2 So, to remember it: think " abc ": a2 + b2 = c2, Sine and Cosine Laws in Triangles. In any triangle we have: 1 - The sine law. sin A / a = sin B / b = sin C / c. 2 - The cosine laws. a 2 = b 2 + c 2 - 2 b c cos A. b 2 = a 2 + c 2 - 2 a c cos B. c 2 = a 2 + b 2 - 2 a b cos C. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.SALE. 10% Off your first order when you sign up for Cosbar email. 1 use today. Get Deal. See Details. 1%. Back. Online Cash Back. 1% Cash Back for Online Purchases Sitewide. Therefore, \(\cos(a + b) = \cos(a) \cos(b) – \sin(a) \sin(b)\) Proved. Cos (A+B) Verification. Need to verify cos(a+b)formula is right or wrong. put the value of a =45° degree and b=30° degree. put the value of a and b in the LHS. cos(a+b) = cos(45°+30°) = cos(75°) = \(\frac{√3 – 1}{2√2}\) put the value of a and b in the RHSMark44 said: If you set sinAcosB + sinBcosA = sinA + sinB, this will be true if cosB = 1 and cosA = 1, which means that A and B can be 0, pi, 2pi, etc. Any integer multiple of pi works. It's much harder to find a solution for cos (A + B) = cosA + cosB, since cos (A + B) = cosAcosB - sinAsinB. I think he means angles besides those (which are ...In any triangle we have: 1 - The sine law sin A / a = sin B / b = sin C / c 2 - The cosine laws a 2 = b 2 + c 2 - 2 b c cos A b 2 = a 2 + c 2 - 2 a c cos B c 2 = a 2 + b 2 - 2 a b cos C Relations Between Trigonometric FunctionsWe would like to show you a description here but the site won’t allow us. Q. sin A + sin B = a and cos A + cos B = b then find the value of cos (A − B) is Q. If sin A + sin B = α and cos A + cos B = β then, write the value of tan ( A + B 2 ) ?Identity 1: The following two results follow from this and the ratio identities. To obtain the first, divide both sides of by ; for the second, divide by . Similarly. Identity 2: The following accounts for all three reciprocal functions. Proof 2: Refer to the triangle diagram above. Note that by Pythagorean theorem .Nov 19, 2017 · 2 Answers Sorted by: 0 Start with cos(A − B) = cos A cos B + sin A sin B cos ( A − B) = cos A cos B + sin A sin B To work out cos(B − A) cos ( B − A), you can proceed in two logical ways. By the first way, you can just transpose (swap) A A and B B in every step. To get: cos(B − A) = cos B cos A + sin B sin A cos ( B − A) = cos B cos A + sin B sin A Oct 7, 2020 · Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have Jul 2, 2020 · Therefore, \(\cos(a + b) = \cos(a) \cos(b) – \sin(a) \sin(b)\) Proved. Cos (A+B) Verification. Need to verify cos(a+b)formula is right or wrong. put the value of a =45° degree and b=30° degree. put the value of a and b in the LHS. cos(a+b) = cos(45°+30°) = cos(75°) = \(\frac{√3 – 1}{2√2}\) put the value of a and b in the RHS For general a and b, we cannot write cos(ab) in terms of the trig functions cosa, sina, cosb, sinb. This is because the trig functions are periodic with period 2π, so adding 2π to b does not change any of these functions. But adding 2π to b can change cos(ab) - for instance, if a = 1 / 2, if sends cos(ab) to − cos(ab).Save $$$ at Cos Bar with coupons and deals like: Get 10% Off with Email Sign Up ~ Refer a Friend: Give $25, Get $25 Off Your Next Order ~ Cos Bar Coupons and Promo Codes for September ~ Get Free Shipping on Orders $100+ ~ Save Up to 60% Off Sale Items ~ and more >>>The formula of cos (A + B) is cos A cos B – sin A sin B. Example : If sin A = 3 5 and cos B = 9 41, find the value of cos (A + B). Solution : We have, sin A = 3 5 and cos B = 9 41. ∴ cos A = 1 – s i n 2 A and sin B = 1 – c o s 2 B. cos A = 1 – 9 25 = 4 5 and sin B = 1 – 81 1681 = 40 41.Step by step video, text & image solution for -cos(A+B)cos(B-A) = by Maths experts to help you in doubts & scoring excellent marks in Class 12 exams. Ab Padhai karo bina ads ke Khareedo DN Pro and dekho sari videos bina kisi ad ki rukaavat ke! The Law of Sines. The Law of Sines (or Sine Rule) is very useful for solving triangles: a sin A = b sin B = c sin C. It works for any triangle: a, b and c are sides. A, B and C are angles. (Side a faces angle A, side b faces angle B and. side c faces angle C). TRIGONOMETRIC IDENTITIES. A N IDENTITY IS AN EQUALITY that is true for any value of the variable. (An equation is an equality that is true only for certain values of the variable.) ( x + 5) ( x − 5) = x2 − 25. The significance of an identity is that, in calculation, we may replace either member with the other.TRIGONOMETRIC IDENTITIES. A N IDENTITY IS AN EQUALITY that is true for any value of the variable. (An equation is an equality that is true only for certain values of the variable.) ( x + 5) ( x − 5) = x2 − 25. The significance of an identity is that, in calculation, we may replace either member with the other.Apr 7, 2023 · 1. 개요 [편집] 삼각형 및 삼각함수 에 관한 정리. 삼각형 \mathrm {ABC} ABC 를 고려하자. 이때 각 A A, B B, C C 의 대변을 각각 a a, b b, c c 라 할 때 다음이 성립한다는 법칙이다. 사인 법칙 과 함께 삼각형의 변의 길이와 각의 크기를 찾을 때 유용한 정리이다. 과거 ... About the Board. The State Board of Cosmetology and Barber Examiners was created in 2005, merging the State Board of Barber Examiners and the State Board of Cosmetology. The licensing of barbers and the barber board was created in 1899, the licensing of cosmetologists began in 1929 and the State Board of Cosmetology was created in 1956.Sin and Cos formulas are given in this article. You can find basic trigonometry formulas, identities, triple angle and double angle formulas. Learn more trigonometry formulas at BYJU'S.코사인 법칙. 기하학 에서 코사인 법칙 (cosine法則, 영어: law of cosines )은 삼각형 의 세 변과 한 각의 코사인 사이에 성립하는 정리이다. 이에 따르면, 삼각형의 두 변의 제곱합에서 사잇각의 코사인과 그 두 변의 곱의 2배를 빼면, 남은 변의 제곱과 같아진다 ... Cos Bar webshop offers customers the opportunity to shop for the best luxury brands in skincare, makeup, fragrance, bath & body, hair, and men products. Customers who are members of Cos Bar get complimentary free shipping and three samples with each of their cos bar skincare product orders. Cos Bar offers loyalty rewards inform of points earned ...Expert Maths Tutoring in the UK - Boost Your Scores with Cuemath. Tan (a - b) is one of the important trigonometric identities, also known as the tangent subtraction formula, used in trigonometry to find the value of the tangent trigonometric function for the difference of angles. We can find the expansion of tan (a - b) to represent the tan of ...In Δ ABC the value of cos B is . What is the trigonometric ratio? Trigonometric ratios can be calculated by taking the ratio of any two sides of the right-angled triangle. The basic Trigonometric ratios are : sin θ = cos θ = tan θ = sec θ = cosec θ = cot θ = According to the question . In Δ ABC , Perpendicular for ∠B = 5 . Base for ...When those side-lengths are expressed in terms of the sin and cos values shown in the figure above, this yields the angle sum trigonometric identity for sine: sin(α + β) = sin α cos β + cos α sin βSin(a - b) can be given as, sin (a - b) = sin a cos b - cos a sin b, where 'a'and 'b' are angles. What is the Formula of Sin (a - b)? The sin(a - b) formula is used to express the sin compound angle formulae in terms of values of sin and cosine trig functions of individual angles.s. Trong lượng giác, Định lý cos (hay công thức cosine, luật cosine hoặc Định lý al-Kashi [1]) biểu diễn sự liên quan giữa chiều dài của các cạnh của một tam giác với cosin của góc tương ứng. Sử dụng các kí hiệu trong Hình 1, ta có thể phát biểu định lý cos dưới dạng ... Sin and Cos formulas are given in this article. You can find basic trigonometry formulas, identities, triple angle and double angle formulas. Learn more trigonometry formulas at BYJU'S. 1. Draw a right-angled triangle with angle A A, opposite side 2 2 and adjacent side 5 5, so that tan A = 25 tan A = 2 5. You should be able to read off the triangle that sin A = 2 29√ sin A = 2 29 and cos A = 5 29√ cos A = 5 29. If B B is in the third quadrant then B − π B − π is in the first quadrant and cos(B − π) = − cos B ...1-855-267-2271. ABOUT US. Since its foundation in Aspen in 1976, Cos Bar is the luxury multi-brand beauty retailer of excellence. Designed for a sophisticated and discerning audience, Cos Bar has successfully carved out a unique and engaging sales experience focused on the needs of the client. Coupled with a carefully curated array of the world ...Voiceover: In the last video we proved the angle addition formula for sine. You could imagine in this video I would like to prove the angle addition for cosine, or in particular, that the cosine of X plus Y, of X plus Y, is equal to the cosine of X. Cosine of X, cosine of Y, cosine of Y minus, so if we have a plus here we're going to have a ... Step by step video, text & image solution for -cos(A+B)cos(B-A) = by Maths experts to help you in doubts & scoring excellent marks in Class 12 exams. Ab Padhai karo bina ads ke Khareedo DN Pro and dekho sari videos bina kisi ad ki rukaavat ke!Aug 28, 2023 · 2 Cos A Cos B is the product to sum trigonometric formulas that are used to rewrite the product of cosines into sum or difference. The 2 cos A cos B formula can help solve integration formulas involving the product of trigonometric ratio such as cosine. sin (A) < a/c, there are two possible triangles. solve for the 2 possible values of the 3rd side b = c*cos (A) ± √ [ a 2 - c 2 sin 2 (A) ] [1] for each set of solutions, use The Law of Cosines to solve for each of the other two angles. present 2 full solutions. Example: sin (A) = a/c, there is one possible triangle.sin A - sin B = 2 cos (A+B)/2 sin (A-B)/2. sin A + sin B = 2 sin (A+B)/2 cos (A-B)/2. sin 2 A - sin 2 B = sin (A+B) sin (A-B) Write tan θ/2 = t. ... then sin θ = 2t / (1 + t 2) ... and cos θ = (1 - t 2) / (1 + t 2) sinh x, cosh x, tanh x. π radians = 180 degrees. 1 radian = 57.3 degrees.SALE. 10% Off your first order when you sign up for Cosbar email. 1 use today. Get Deal. See Details. 1%. Back. Online Cash Back. 1% Cash Back for Online Purchases Sitewide. We would like to show you a description here but the site won’t allow us.Case of acute angle γ, where a < 2b cos γ. Drop the perpendicular from A onto a = BC, creating a line segment of length b cos γ. Duplicate the right triangle to form the isosceles triangle ACP. Construct the circle with center A and radius b, and a chord through B perpendicular to c = AB, half of which is h = BH. Apply the Pythagorean ... v t e In trigonometry, trigonometric identities are equalities that involve trigonometric functions and are true for every value of the occurring variables for which both sides of the equality are defined. Geometrically, these are identities involving certain functions of one or more angles. Tom Ford – Cos Bar. 103 products. Eye Color Quad. Tom Ford. [11 colors available] $90.00. Eye Color Quad. Tom Ford.2 Cos A Cos B is the product to sum trigonometric formulas that are used to rewrite the product of cosines into sum or difference. The 2 cos A cos B formula can help solve integration formulas involving the product of trigonometric ratio such as cosine.Trigonometric Identities are the equalities that involve trigonometry functions and holds true for all the values of variables given in the equation. There are various distinct trigonometric identities involving the side length as well as the angle of a triangle. The trigonometric identities hold true only for the right-angle triangle. The following (particularly the first of the three below) are called "Pythagorean" identities. sin 2 ( t) + cos 2 ( t) = 1. tan 2 ( t) + 1 = sec 2 ( t) 1 + cot 2 ( t) = csc 2 ( t) Advertisement. Note that the three identities above all involve squaring and the number 1. You can see the Pythagorean-Thereom relationship clearly if you consider ... Doubtnut is No.1 Study App and Learning App with Instant Video Solutions for NCERT Class 6, Class 7, Class 8, Class 9, Class 10, Class 11 and Class 12, IIT JEE prep, NEET preparation and CBSE, UP Board, Bihar Board, Rajasthan Board, MP Board, Telangana Board etcCos Bar General Information. Description. Retailer of cosmetic products based in Los Angles, California. The company offers luxury cosmetics and skincare boutique featuring products for both men and women, enabling clients to take care of their body and maintain a standard of living.Get an answer for 'if cos(A-B) + cos(B-C) + cos(C-A) = -3/2 Prove cos A + cos B + cos C = sin A + sin B + sin C = 0' and find homework help for other Math questions at eNotes Select an area of the ...Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.Nov 23, 2009 · Mark44 said: If you set sinAcosB + sinBcosA = sinA + sinB, this will be true if cosB = 1 and cosA = 1, which means that A and B can be 0, pi, 2pi, etc. Any integer multiple of pi works. It's much harder to find a solution for cos (A + B) = cosA + cosB, since cos (A + B) = cosAcosB - sinAsinB. I think he means angles besides those (which are ... Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more. Cos Bar is the premier luxury multi-brand beauty retailer, carrying a hand-picked, curated array of the world's best beauty brands with trusted experts who have years of experience in the beauty industry committed to delivery the world's best beauty buying experience. Sisley-Paris, Chantecaille, Cle de Peau and more.cos a cos b = (1/2) [cos (a + b) + cos (a - b)] It is applied when either the two angles a and b are known or when the sum and difference of angles are known. The cos a cos b formula helps in solving integration formulas and problems involving the product of trigonometric ratio such as cosine.Example 2: Express 6 cos x cos 2x in terms of sum function. Solution: Consider, 6 cos x cos 2x = 3 [2 cos x cos 2x] Using the formula 2 cos A cos B = cos (A + B) + cos (A – B), = 3[cos (x + 2x) + cos (x – 2x)] = 3[cos 3x + cos (-x)] = 3 [cos 3x + cos x] To learn other trigonometric formulas Register yourself at BYJU’S.Mark44 said: If you set sinAcosB + sinBcosA = sinA + sinB, this will be true if cosB = 1 and cosA = 1, which means that A and B can be 0, pi, 2pi, etc. Any integer multiple of pi works. It's much harder to find a solution for cos (A + B) = cosA + cosB, since cos (A + B) = cosAcosB - sinAsinB. I think he means angles besides those (which are ...s. Trong lượng giác, Định lý cos (hay công thức cosine, luật cosine hoặc Định lý al-Kashi [1]) biểu diễn sự liên quan giữa chiều dài của các cạnh của một tam giác với cosin của góc tương ứng. Sử dụng các kí hiệu trong Hình 1, ta có thể phát biểu định lý cos dưới dạng ... Mission Overview. COS-B, an ESA mission, was launched from NASA’s Western Test Range by a Thor Delta vehicle on 9 August 1975. Its scientific mission was to study in detail the sources of extraterrestrial gamma radiation at energies above about 30 MeV. COS-B operated in a pointing mode with its spin axis directed towards fixed points in the sky. Formulas from Trigonometry: sin 2A+cos A= 1 sin(A B) = sinAcosB cosAsinB cos(A B) = cosAcosB tansinAsinB tan(A B) = A tanB 1 tanAtanB sin2A= 2sinAcosA cos2A= cos2 A sin2 A tan2A= 2tanA2 Cos a Cos b = Cos (a + b) + Cos (a – b) In mathematics, there are a total of six trigonometric functions of angles, which are cited below: Sine; Cosine; Tangent; Cotangent; Secant; Cosecant; What do you mean by 2 Cos a Cos b? The formula of 2 Cos a Cos b is – Cos (a + b) + Cos (a – b) = 2 Cos a Cos b.Sin(a - b) can be given as, sin (a - b) = sin a cos b - cos a sin b, where 'a'and 'b' are angles. What is the Formula of Sin (a - b)? The sin(a - b) formula is used to express the sin compound angle formulae in terms of values of sin and cosine trig functions of individual angles.Sine and Cosine Laws in Triangles. In any triangle we have: 1 - The sine law. sin A / a = sin B / b = sin C / c. 2 - The cosine laws. a 2 = b 2 + c 2 - 2 b c cos A. b 2 = a 2 + c 2 - 2 a c cos B. c 2 = a 2 + b 2 - 2 a b cos C. Voiceover: In the last video we proved the angle addition formula for sine. You could imagine in this video I would like to prove the angle addition for cosine, or in particular, that the cosine of X plus Y, of X plus Y, is equal to the cosine of X. Cosine of X, cosine of Y, cosine of Y minus, so if we have a plus here we're going to have a ...In any triangle ABC, prove that: a3 cos(B−C)+b3 cos(C −A)+ c3 cos(A− B) = 3abc. If the sides of a ΔABC are a = 4, b = 6 and c = 8, show that 4cosB+3cosC = 2. In ABCshow thata3cos(B−C)+b3cos(C −A)+ c3cos(A− B) = 3abc. In a ΔABC prove that: a3cos(B−C)+b3cos(C −A)+ c3cos(A− B) = 3abc.1-855-267-2271 Cos Bar USA, Inc. 11022 Santa Monica Blvd, Suite 290 Los Angeles, CA 90025 Compared to y=cos(x), shown in purple below, the function y=2 cos(x) (red) has an amplitude that is twice that of the original cosine graph. B—used to determine the period of the function; the period of a function is the distance from peak to peak (or any point on the graph to the next matching point) and can be found as . In y=cos(x ... Example 2: Express 6 cos x cos 2x in terms of sum function. Solution: Consider, 6 cos x cos 2x = 3 [2 cos x cos 2x] Using the formula 2 cos A cos B = cos (A + B) + cos (A – B), = 3[cos (x + 2x) + cos (x – 2x)] = 3[cos 3x + cos (-x)] = 3 [cos 3x + cos x] To learn other trigonometric formulas Register yourself at BYJU’S.
2 cos A⋅cos B = cos(A + B) + cos(A - B) 2 sin A⋅sin B = cos(A - B) - cos(A + B) Half, Double, and Triple-Angles Trigonometric Ratios Identities. Double Angle Trigonometric Ratios Identities. The double angle trigonometric identities can be obtained by using the sum and difference formulas. For example, from the above formula sin (A+B) = sin .... Muzzleloader kit cabela
23 reviews of Cos Bar Brentwood "Great Service from Ms. Devin Patterson and Donna. The store is clean and well-organized, and the Staff will help you with a beautiful smile.Cos Bar. 7,585 likes · 32 talking about this · 170 were here. Welcome to the Official Cos Bar Facebook Page. Discover more at www.cosbar.com 1-855-267-2271 Cos Bar USA, Inc. 11022 Santa Monica Blvd, Suite 290 Los Angeles, CA 90025We can give the proof of Cos A + Cos B trigonometric formula using the expansion of cos (A + B) and cos (A - B) formula. As we stated in the previous section, we write Cos A + Cos B = 2 cos ½ (A + B) cos ½ (A - B). Let us assume that (α + β) = A and (α - β) = B.Nov 19, 2017 · 2 Answers Sorted by: 0 Start with cos(A − B) = cos A cos B + sin A sin B cos ( A − B) = cos A cos B + sin A sin B To work out cos(B − A) cos ( B − A), you can proceed in two logical ways. By the first way, you can just transpose (swap) A A and B B in every step. To get: cos(B − A) = cos B cos A + sin B sin A cos ( B − A) = cos B cos A + sin B sin A 2 cos A⋅cos B = cos(A + B) + cos(A - B) 2 sin A⋅sin B = cos(A - B) - cos(A + B) Half, Double, and Triple-Angles Trigonometric Ratios Identities. Double Angle Trigonometric Ratios Identities. The double angle trigonometric identities can be obtained by using the sum and difference formulas. For example, from the above formula sin (A+B) = sin ...If cos θ = 1, cos θ = 1, then both vectors have the same direction. If cos θ = 0, cos θ = 0, then the vectors, when placed in standard position, form a right angle (Figure 2.46). We can formalize this result into a theorem regarding orthogonal (perpendicular) vectors. If cos θ = 1, cos θ = 1, then both vectors have the same direction. If cos θ = 0, cos θ = 0, then the vectors, when placed in standard position, form a right angle (Figure 2.46). We can formalize this result into a theorem regarding orthogonal (perpendicular) vectors. Oct 7, 2020 · Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have May 9, 2014 · For general a and b, we cannot write cos(ab) in terms of the trig functions cosa, sina, cosb, sinb. This is because the trig functions are periodic with period 2π, so adding 2π to b does not change any of these functions. But adding 2π to b can change cos(ab) - for instance, if a = 1 / 2, if sends cos(ab) to − cos(ab). 38K Followers, 1,078 Following, 3,190 Posts - See Instagram photos and videos from Cos Bar (@cosbar)Click here👆to get an answer to your question ️ cos(A + B)cos(A - B) is equal to .
