Question

Rewrite with only sin x and cos x.
sin 3x - cos x

Answer 1

Hint sin2x = 2sinxcosx

Answer 2

Can you help me? This confuses me too much

Answer 3

how far have you got with trigonometry?

Answer 4

sorry i have to go now

Answer 5

do you know any trig identities for multiple of an angle?

Answer 6

here is the one that is worth memorizing:
sin(3x) = -4sin^3(x) + 3sin(x)

Answer 7

Okay an you help me solve this

Answer 8

@sourwing

Answer 9

you're practically done.
sin(3x) - cos(x) = sin(3x) = -4sin^3(x) + 3sin(x) - cos(x)

Answer 10

A. 2 sin x - sin^3 x - cos x
B. 2 sin x cos^2 x + sin x - 2 sin ^3 x - cos x
C. 2 sin^3 x cos^4 x + 1
D. 3 sin x cos x - sin^3 x - cos x

Answer 11

I think it's D @sourwing

Answer 12

sin3x = sin(2x + x) = sin2xcosx + sinxcos2x
= 2sinxcos^2x + sinx( cos^2x - sin^2x)
= 2sinxcos^2x + sinxcos^2x - sin^3x
= 3sinx cos^2x - sin^3x

sin3x - cosx = 3sinx cos^2x - sin^3x - cosx

Answer 13

- that result works though its not exactly = D