# Math Help - Help proving this expression is equal..

1. ## Help proving this expression is equal..

Prove that [sin x + cos x]^2 = 1 + sin 2x

2. Originally Posted by Manizzle
Prove that [sin x + cos x] = 1 + sin 2x
I think you mean ...

$(\sin{x} + \cos{x})^2 = 1 + \sin(2x)$

3. If that's not what he means then his book must be wrong.

4. yes i'm sorry thats what i meant, my superscript didn't work with the font i had on here sorry guys

5. $(\sin{x} + \cos{x})^2 = 1 + \sin(2x)$

square the left side ...

$\sin^2{x} + 2\sin{x}\cos{x} + \cos^2{x}$

rearrange a bit ...

$(\sin^2{x} + \cos^2{x}) + 2\sin{x}\cos{x}$

now, you should know what the sum of the first two terms is ... also, look up the double angle formula for sine to deal with the last term.