Cot^2 x -Cot x =0 factor out Cot x from each term
Cot x(cot x -1) =0
Cot x =0 and Cot x =1 Remember cot is cos/sin
For Cot x =0 this will occur wherever cosine x is zero which is at pi/2 and 3pi/2 If sin=0 the function is undefined
For Cot x= 1 this will occur wherever sin equals cosine which is pi/4 and 5pi/4