posted by Tom .
3. (1/1+cos s)=csc^2 s-csc s cot s
sinx/cscx is the same thing as sin^2 x
cosx/secx is the same thing as cos^2 x
What you you know about the sum of sin^2 and cos^2 ?
Try proving the other identities yourself, writing tan, csc and sec in terms of sin and cos.