How to find all values of $x$ for which $\sec x=-1$ is true?

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Find all values of x for which the following is true. $\sec x = -1$

a) π + 2kπ b) (π/4) + 2kπ c) 2kπ d) (π/2) + kπ e) -(π/3) + 2kπ

I know that $\sec \theta =\frac 1 {\cos \theta}$. I don't know what to do after that. I think the unit circle is involved somehow.

This is for my online trigonometry class, it's a homework problem and I can't figure it out. Any help is much appreciated.

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1 Answer

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$\sec x=-1\iff\cos x=-1\iff x\equiv \pi\mod2\pi$.

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