Use the basic identities to simplify

(1-sin^2 theta)/ (csc^2 theta - 1)

(1 - sin^2 Ø)/(1/sin^2 Ø - 1)

= (1- sin^2 Ø)/( (1 - sin^2 Ø)/sin^2 Ø )
= (1 - sin^2 Ø) (sin^2 Ø)/(1 - sin^2 Ø)
= sin^2 Ø