How do you evaluate $cos(arccos(-1))$ ?

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Answer 1 · 2016-04-26T08:37:46

$-1$

cosine and arc cosine are each inverse of the other function.

Verbally, $'cos arc cos (-1)'$ is 'cosine of the angle whose cosine is $-1$ '.

If $y = f(x), x = f^(-1)y, f(f^(-1)(y))=y and f^(-1)(f(x)) = x$

Here, $cos(cos^(-1)(-1))=-1$ .. Also, $cos^(-1) cos pi=pi$ .

How do you evaluate cos(arccos(-1))cos(arccos(-1))?