How do you find the exact value of $arctan [cos(-5pi/6)]$ ?

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Answer 1 · 2016-03-14T05:18:15

$40.893^o$ or $0.714$ radians

As $cos(-5pi/6)=-sqrt3/2=-0.866$ ,

$arctan[cos(-5pi/6)]$ is an angle $theta$ so that

$tantheta=-0.866$ and

$theta=arctan(-0.866)=40.893^o$ or $0.714$ radians

How do you find the exact value of arctan [cos(-5pi/6)]arctan [cos(-5pi/6)]?