Question

1 + cos 4A =?
pls tell fast ​

Answer 1

Answer:2A

Step-by-step explanation:

Answer 2

Step-by-step explanation:

$\cos(4 \alpha ) = \cos(3 \alpha + \alpha )$

$= \cos(3 \alpha ) \cos( \alpha ) - \sin(3 \alpha ) \sin( \alpha )$

$= (4cos^{3} ( \alpha ) - 3 \cos( \alpha ) ) (cos( \alpha ) ) - (3 \sin( \alpha ) - 4 \sin ^{3} ( \alpha ))( \sin( \alpha ))$

$4 \cos ^{4} ( \alpha ) - 3 \cos^{2} ( \alpha ) - 3 \sin^{2} ( \alpha ) + 4 \sin ^{4} ( \alpha )$

$4( \sin^{4} ( \alpha ) + \cos ^{4} ( \alpha ) ) - 3( \sin {}^{2} ( \alpha ) + \cos {}^{2} ( \alpha ) )$

$4(1 - 2\sin {}^{2} ( \alpha ) \cos {}^{2} ( \alpha ) ) - 3$

$4 - 8 \sin {}^{2} ( \alpha ) \cos {}^{2} ( \alpha ) - 3$

$1 - 8 \sin {}^{2} ( \alpha) \cos {}^{2} ( \alpha )$