# Thread: Solving for 0 ≤ x ≤ 360

1. ## Solving for 0 ≤ x ≤ 360

Oh man I suck at these. Can anyone help out please?

Solve the following equations for 0 ≤ x ≤ 360

a) $\displaystyle sin2x + sinx = 0$

b) $\displaystyle 3cos2x + 2 + cosx = 0$

A kind of method would be fantastic, Thanks guys!

2. Hello

Originally Posted by Nick87
Oh man I suck at these. Can anyone help out please?

Solve the following equations for 0 ≤ x ≤ 360

a) $\displaystyle sin2x + sinx = 0$
Remember that $\displaystyle \sin 2x=2 \sin x \cos x$

$\displaystyle 2 \sin x \cos x+ \sin x=0$

Factor by $\displaystyle \sin x$ :

$\displaystyle \sin x (2 \cos x+1)=0$

So either $\displaystyle \sin x=0$, either $\displaystyle 2 \cos x+1=0$

b) $\displaystyle 3cos2x + 2 + cosx = 0$
note that $\displaystyle \cos 2x=2 \cos^2 x-1$.

Then substitute $\displaystyle t=\cos x$ and solve for t

A kind of method would be fantastic, Thanks guys!
We have someone fantastic around here

3. We sure do. Thanks Moo!