## anonymous 5 years ago use de moivre's formula with n= 2 to find trigonometric identities cos2theta and sin 2theta plz help me.....:(

1. anonymous

farily simple

2. anonymous

fairly lol

3. anonymous

$(\cos(\theta) + isin(\theta))^n = cos(n \theta) +isin(n \theta ) )$

4. watchmath

$$\cos (2\theta)_1\sin(2\theta)=(\cos \theta +i \sin \theta)^2=(\cos^2\theta-sin^2\theta)+i(2\sin\theta\cos\theta)$$

5. anonymous

^ that yeh :|

6. watchmath

The left most expression should be $$\cos(2\theta)+i\sin(2\theta)$$

7. anonymous

there is actually something to do here yes? besides using laws of exponents i mean.

8. anonymous

oops my apologies whatchmath wrote it. should should also mumble something about setting real part = real part and imaginary part = imaginary part.

9. anonymous

watchmath i mean. yikes it is early

10. watchmath

Are you in US too satellite?

11. anonymous

yes US

12. anonymous

trying to learn latex and practicing here as much as i can