1.

The principal value of `cot^(-1)(-1)` isA. `-pi/4`B. `pi/4`C. `(5pi)/4`D. `(3pi)/4`

Answer» Correct Answer - D
Let `cos^(-1)(-1)=x`, where `x in [0,pi]`.
Then, `cotx=-1=-cotpi/4=cot(pi-pi/4)=cot(3pi)/4 rArr x=(3pi)/4`.


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