Since you have the sign of a sum try the sum identity for sins#2
sin(x + pi/2)= cos x
replace tan and sec with their definitions in terms of sins and cosines and simplify#3
tan^2(x) = sec^2(x)= sin^2(x) - cos^2(x)
This is equivalent to:#4
cot(x)/(1 + csc(x)) = (csc(x) - 1)/ cot(x)
Now replace everything with its definition in terms of sins and cosins and simplify both sides.