Question 766717
Use the fundamental identities to find an equivalent expression involving only sines and cosines and then simplify it. 
(1-cscx)(1+cscx)
difference of squares
{{{1-csc^2(x)=1-1/sin^2(x)=(sin^2(x)-1)/(sin^2(x))=-cos^2(x)/(sin^2(x))}}}=-cot^2(x)