Verify the identity:
tan^2 x+1/ tan^2 x= csc^2 x

Take note that tan^{2}(x)+1=sec^{2}(x)=\frac{1}{cos^{2}(x)} and

tan^{2}(x)=\frac{sin^{2}(x)}{cos^{2}(x)}

Make the substitutions and it should fall into place.