What is the formula of cos2(A+B) and cos2(A-B)
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Solution

$\cos 2 (A + B) = \cos^{2} (A + B) - \sin^{2} (A + B) [As, \cos 2 x = \cos^{2} x - \sin^{2} x] \cos 2 (A + B) = 2 \cos^{2} (A + B) - 1 [As, \sin^{2} x + \cos^{2} x = 1] \cos 2 (A + B) = 1 - 2 \sin^{2} (A + B) [As, \sin^{2} x + \cos^{2} x = 1] \cos (2 A + 2 B) = \cos 2 A . \cos 2 B - \sin 2 A . \sin 2 B [as, \cos (x + y) = \cos x . \cos y - \sin x \sin y] \cos 2 (A - B) = \cos^{2} (A - B) - \sin^{2} (A - B) [As, \cos 2 x = \cos^{2} x - \sin^{2} x] \cos 2 (A - B) = 2 \cos^{2} (A - B) - 1 [As, \sin^{2} x + \cos^{2} x = 1] \cos 2 (A - B) = 1 - 2 \sin^{2} (A - B) [As, \sin^{2} x + \cos^{2} x = 1] \cos (2 A - 2 B) = \cos 2 A . \cos 2 B + \sin 2 A . \sin 2 B [as, \cos (x - y) = \cos x . \cos y + \sin x \sin y]$

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Similar questions

\frac{cos 2 B + cos 2 A}{cos 2 B - cos 2 A} = cot (A + B) cot (A - B)

$\frac{c o s^{2} B - c o s^{2} C}{b + c} + \frac{c o s^{2} C - c o s^{2} A}{c + a} + \frac{c o s^{2} A - c o s^{2} B}{a + b} = 0$

{cos}^{2} A + {cos}^{2} B - 2 cos A cos B cos (A + B) - {sin}^{2} (A + B)

{cos}^{2} A + {cos}^{2} (A + \frac{2 π}{3}) + {cos}^{2} (A - \frac{2 π}{3}) =

{cos}^{2} A + {cos}^{2} B - 2 cos A cos B cos (A + B) = s i n^{2} (A + B)

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