Question

Rewrite with only sin x and cos x.

cos 2x - sin x

Answer 1

is it cos2x - sin2x - sin x ?

Answer 2

Use the double angle formula: Cos(2x) = cos^2 x - sin^2 x
It's a trig identity, so you just have to memorize it.
Here's a helpful website:
http://www.sosmath.com/trig/Trig5/trig5/trig5.html

Answer 3

Does that help?

Answer 4

@Nanoman Ah, so I would have cos^2x - sin^2x - sin x?

Answer 5

Yes, but keep track of your notation. It looks like you're saying cos^(2x) -sin^(2x). I should have said cos^2 (x) -sin^2 (x) so you wouldn't be confused.

Answer 6

Ok I understand that. And that would be my final answer correct?

Answer 7

You can also simplify the term "cos^2 (x) -sin^2 (x)" as shown on the site, but I don't think you'll need to. You want it in terms of cos(x), so this would be correct. Just to be safe, you can convert cos^2 (x) to (cosx)^2. The two are equivalent, and you can do the same thing with any trig function.

Answer 8

@Nanoman perfect thanks a lot:)

Answer 9

No problem!