Question 929066
Verify the identity: 
{{{(1 - cos x) / (1 + cos  x) = (cot x - csc x)^2}}}
Start with right side:
{{{(cotx-cscx)^2=cot^2(x)-2cotxcscx+csc^2(x)
=cos^2(x)/sin^2(x)-2cosx/sinx*1/sinx+1/sin^2(x)
=(cos^2(x)-2cosx+1)/(sin^2(x))
=(cosx-1)^2/(1-cos^2(x))
=(cosx-1)^2/(1-cos^2(x))}}}
(1-cosx)^2/(1+cosx)(1-cosx)=(1-cosx)/(1+cosx)
verified: right side=left side
note:(cosx-1)^2=(1-cosx)^2