# How do you solve #2cos^2x+cosx -1=0# for #0<=x<=2pi#?

##### 1 Answer

Jun 21, 2018

#### Explanation:

Solve this quadratic equation for cos x.

Since a - b + c = 0, use shortcut. The 2 real roots are:

cos x = -1, and

a. cos x = -1

Unit circle gives:

b.

Trig table and unit circle give -->

Note.

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