[tex]cos(-\frac{\pi }{4} )=cos(\frac{\pi }{4} )[/tex] illustrates why cosine is an even function.
What is an even function?
A function such that f(x)=f(−x) where the value remains unchanged if the sign of the independent variable is reversed.
According to the question
Cosine is an even function
If f(x) is an even function, then f(x) = f(-x)
So, [tex]cos(-\frac{\pi }{4} )=cos(\frac{\pi }{4} )[/tex] illustrates why cosine is an even function.
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