The identity `(1 + csc x)/sec x - cot x = cos x` has to be proved.
`(1 + csc x)/sec x - cot x`
=> `(1 + 1/sin x)/(1/cos x) - (cos x)/(sin x)`
=> `(cos x + cos x/sin x) - (cos x)/(sin x)`
=> `cos x + cos x/sin x - (cos x)/(sin x)`
=> `cos x`
This proves that `(1 + csc x)/sec x - cot x = cos x`