Why is \cos(-pi/6) the same as \cos(pi/6)?

Why is $$\displaystyle{\cos{{\left(-\frac{\pi}{{6}}\right)}}}$$ the same as $$\displaystyle{\cos{{\left(\frac{\pi}{{6}}\right)}}}$$?

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zurilomk4
The cosine function is even. This means that $$\displaystyle{\cos{{\left(-\frac{\pi}{{6}}\right)}}}$$ is the same thing as $$\displaystyle{\cos{{\left(\frac{\pi}{{6}}\right)}}}$$.
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SlabydouluS62
$$\displaystyle{\cos{{\left(-{x}\right)}}}={\cos{{\left({x}\right)}}}$$ as the cos function is even.