Remember the basic trig identity
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We can move the cosine term to the right side to get

We can then replace

in the original equation and basically factor the resulting equation like a quadratic:





Then, we can see that

either equals

or

. But since the range of cosine is only from
![[-1, 1]](https://tex.z-dn.net/?f=%5B-1%2C%201%5D)
, cosine can't equal

at all! So, you just have to solve for x when

, which is when

(The last part of the solution says that k can be any integer.)
If you only want solutions in the range

, then your answer is just