Question

Find the exact value of the trigonometric function. Do not use a calculator. cot (−5pi/4)

Answer 1

 we know that

−5pi/4----------> -1.25 pi---------> belong to the third quadrant

1.25 pi-------> (pi+pi/4)
cot (−5pi/4)=-cot (pi/4)
pi/4=45°
cot (45°)=1
then 
cot (pi/4)=1
cot (−5pi/4)=-1-----------> is negative because belong to the third quadrant

the answer is
cot (−5pi/4)=-1