Question

Rewrite with only sin x and cos x.

cos 3x

Answer 1

\[\cos(3x) = \cos(1.5x + 1.5x)\]Use\[\cos(a + b) = \cos(a)\cos(b) - \sin(a)\sin(b)\]

Answer 2

2 sin2x cos x - 2 sin x cos x be my answer

Answer 3

but that has sin2x in it ??

Answer 4

Rather, use \(\cos(2x) = \cos^2 (x) - \sin^2(x)\)

Answer 5

Here, \(x = 1.5x\).

Answer 6

-sin3x + 2 sin x cos x

Answer 7

Hmm! I think that doesn't work.

Answer 8

cos x - 4 cos x sin2x

Answer 9

\[\cos(x + 2x) = \cos(x)\cos(2x) - \sin(x)\sin(2x)\]So you can use the formulas for \(\sin(2x)\) and \(\cos(2x)\)

Answer 10

-sin2x + 2 sin x cos x

Answer 11

is my answer

Answer 12

But that has \(2x\) in it

Answer 13

These are my choices, one of them has to fit
cos x - 4 cos x sin2x

-sin3x + 2 sin x cos x

-sin2x + 2 sin x cos x

2 sin2x cos x - 2 sin x cos x