First, apply the rule of difference of squares
x^2-y^2 = (x+y)(x-y)
sin^2-1 = (sinx + 1)(sinx-1) = (sinx + 1)(sinx-1)/tanxsinx-tanx
From here, you need to cancel the common factor of sinx-1. This gives you:
sinx+1/tanx
This gives you the answer because both sides are now equal. This equality is a trigonometric identity.
Hope I helped!
