Question

1+cos(8x)
I need help step by step.

Answer 1

What do you want to do? Please, take a snapshot or post the original problem.

Answer 2

The problem is simply that equation. Nothing else.

Answer 3

So what is the question?

Answer 4

I will need to solve it using one of the trig functions,,.

Answer 5

Possible answers:
4sin(2x)
4cos(2x)
2sin^2(4x)
2cos^2(4x)

Answer 6

ok, just 2cos^2 (4x)

Answer 7

I know the answer because I just got it corrected, but I don't know why thats the answer.

Answer 8

oh, so you have to open your book and read the proof from the book. To solve the problem, we just apply the proven result. We don't prove it again.

Answer 9

Now, the step is
cos (2x) = 2 cos^2 (x) +1
So if you ask me how, then I have to prove it first , then apply to your problem.
but to prove this guy, you need another guy, at the end up, I have to prove all of identity. Ha!!!

Answer 10

Is it necessary to memorize every single trig identity?

Answer 11

Well maybe not necessary but certainly helpful, as some can take a long time to derive.

Answer 12

I think so!! an identity is an ID for a particular problem. You are better memorize some.

Answer 13

Please explain the steop where you got cos(2x)= 2 cos^2 (x) +1

Answer 14

Is it just from the identities?

Answer 15

cos (2x)= 2cos^2x -1, not +1

Answer 16

http://www.themathpage.com/atrig/double-proof.htm
read it, all proofs are there

Answer 17

where did the 8 go?

Answer 18

oh, on half angle, if \(cos(\color{red}{2}x)= 2cos^2(\color{red}{1}x)-1\)

then if the red part is 8 from the LHS, the red part from the RHS is 4 (a half of the LHS)

that is \(cos(\color{red}{8}x)= 2cos^2(\color{red}{4}x)-1\)