Prove that $$(1−x)^2\frac{d^2y}{dx^2}−x\frac{dy}{dx}+p^2y=0 $$

where $$y = \sin(pt)$$ and $$ x =\sin(t) $$

please, tell me how this makes sense, shouldn't the second derivative be $0$?

I am wrestling with this every day for about a month and can't make sense of it.