Practice!

Sample Problem

Find all solutions of 2cos2x+cos x-1=0 on the interval [0, 2π).

Solution

2cos2x+cosx-1=0 : Factor this quadratic equation

(2cosx-1)(cosx+1)=0

2cosx-1=0 or cosx+1=0

Cosx=1/2 or cosx=-1

Cos x=1/2 à x=π/3, 5π/3

Cos x=-1 , x=π