Hello

Im having problems to solve the following trig equation.

$\displaystyle cosx-\frac{\frac{1}{2}}{cosx}=\frac{1}{2}$

Im given the following information

$\displaystyle x_{1}=2n\pi$

$\displaystyle x_{2}=\frac{a\pi }{b}+2n\pi $

$\displaystyle x_{3}=\frac{c\pi }{d}+2n\pi $

0 < $\displaystyle \frac{a\pi }{b}+2n\pi$ < $\displaystyle \frac{c\pi }{d}+2n\pi$ < $\displaystyle 2\pi$

where n are integers

im not allowed to use a calculator, so im unsure how to eaven start...