Transform the given equation into polynomial form using the fact that
Write this quadratic equation in standard form by dividing by 2
Solve the quadratic equation by completing the square. Add 1/2 to both sides
Take half the coefficient of
Factor the left-hand side.
An alternative and a few details.
One might also use the Quadratic Formula.
After the step
Now observe that
When we write
In the third quadrant, the angle with the same reference angle as
The solutions to the equation are
Since cosine is an even function, [