# How do you find all solutions of the equation in the interval (0, 2pi) #2cos^2 theta+cos theta = 0#?

##### 1 Answer

Apr 12, 2016

Factor out a cos.

#### Explanation:

cos is negative in quadrants II and III. Applying the 30-60-90 special triangle and reference angles (leave a question on my homepage if you don't know how these work), we find that

Thus, your solution set is

Hopefully this helps!