Question

1+cos(8x)=
A. 4cos(2x)
B. 2sin^2(4x)
C.4sin(2x)
D.2cos^(4x)

Answer 1

cos 2x=1-2sin^2x

Answer 2

use this

Answer 3

Try using \(\large cos^2x = \frac{1}{2} (1+cos(2x)) \)

Answer 4

but how would I use it?

Answer 5

there is another identity... cos2x=2cos^2x-1

Answer 6

I'm sorry, I'm really confused

Answer 7

Answer is D, see how....

Answer 8

cos2x=2cos^2x-1
=>1+cos2x=2cos^2x

now instead of 2x put 8x(left side) so in the right side its half of 8 that is 4.
Got it?

Answer 9

yeah, i think so. thanks!

Answer 10

My pleasure