Question

How are these solved?

1. cosx+1=0; x ∈ R
2. 4sin^2 x - 1 = 0; x ∈ R
3. 2cos^2 x + 3cosx + 1 =0;0 ≤ x < 2π

Answer 1

cosx+1 = 0
cosx = -1

4sin^2x-1 = 0
sinx = ±1/2

2cos^2x+3cosx+1 = 0
(2cosx+1)(cosx+1) = 0
cosx = -1/2 or -1

Now find angles in the proper quadrants for those solutions.
And don't forget your Algebra I now that you're doing trig!