Use the Addition Formula for Sine to prove the Double-Angle Formula for Sine.
sin 2x = 2 sin(x) cos(x)
Rewrite 2x as x + x, and use the Addition Formula for Sine to simplify.
sin 2x= sin(x + x)

Question

anonymous · Answer

oh, right. do exactly what it says. replace x + y in the formula by x + x and write what you have, it will give you exactly what you want.

anonymous · Answer

first write 
$$\sin(x+y)=\sin(x)\cos(y)+\cos(x)\sin(y)$$ then put and x everywhere you see a y and you will get the answer.

anonymous · Answer

I still don't understand it.

anonymous · Answer

try what i wrote above and see what happens.  it is clear that 
$$x+x=2x$$ right?  so if you  have a formula for 
$$\sin(x+y)$$ you can make one for 
$$\sin(x+x)$$

anonymous · Answer

Ok!

anonymous · Answer

if you are still confused after you do it write again, but i bet it will work out on the first try

anonymous · Answer

sin (x+y) = cos x sin x + cos x sin x = cos^2 x + sin^2 x