\

The trigonometric equation is .

\

The cosine function is negative in second and third quadrant.

\

In second quadrant ,

\

\

\

\

General solution: If cos(θ) = cos(α), then θ = 2nπ ± α, where n is an integer.

\

The cosine function is negative in second and third quadrant.

\

The general solution is . \ \

\