How do you evaluate $arctan(-sqrt3/3)$ without a calculator?

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Answer 1 · 2016-09-16T10:44:28

$-pi/6$

$tan^-1(-sqrt3/3)= -pi/6$ .Since $tan(-pi/6)=-sqrt3/3$ and $-pi/6 in (-pi/2 , pi/2)$ [Ans]

How do you evaluate arctan(-sqrt3/3)arctan(-sqrt3/3) without a calculator?