Question

Prove: sin θ - sin θ•cos2 θ = sin3 θ. You must show all work.

Answer 1

idk even where to begin

Answer 2

Just thought
Maybe you can take the right hand side and show the left hand side

Try to play with this thought:
sin(3x) is sin(2x+x)

Answer 3

That should be a hint to use the sum identity for sin

Answer 4

Memorize the identities for cos 2*theta

Answer 5

Though I could be wrong but I don't think this is an identity.

Answer 6

One way to find out is to find a counterexample

Answer 7

try theta=pi/2
does not work

Answer 8

sin(2x)=2*sin(x)*cos(x)

Answer 9

cos(2x)=2cos^2 (x)-1

Answer 10

Maybe the problem has been written incorrectly.

Answer 11

Unless the instructions say to:
Prove if true and give a counterexample if false.
If so then I have accidentally given you the answer.

Answer 12

cos(2x)=1-2sin^2 (x)
so what's sin(x)*cos(2x)?