How do you find the exact value of $cos^-1(cos(pi/7))$ ?

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Answer 1 · 2017-02-02T17:10:38

$cos^(-1)(cos(pi/7))=pi/7$

As per definition of $cos^(-1)$ , if $cosa=x$ , $a=cos^(-1)x$

In the given problem, let $cos(pi/7)=v$

then as per definition $cos^(-1)v=pi/7$ .................(1)

and putting value of $v=cos(pi/7)$ in (1), we get

$cos^(-1)(cos(pi/7))=pi/7$

How do you find the exact value of cos^-1(cos(pi/7))cos^-1(cos(pi/7))?