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

Question

anonymous · Answer

idk even where to begin

myininaya · Answer

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)

myininaya · Answer

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

idealist10 · Answer

Memorize the identities for cos 2*theta

myininaya · Answer

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

myininaya · Answer

One way to find out is to find a counterexample

myininaya · Answer

try theta=pi/2
does not work

idealist10 · Answer

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

idealist10 · Answer

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

myininaya · Answer

Maybe the problem has been written incorrectly.

myininaya · Answer

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

idealist10 · Answer

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