[tex]\bf sin(x)[csc(x)-sin(x)]~~=~~cos^2(x) \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ sin(x)\left[\cfrac{1}{sin(x)}-\cfrac{sin(x)}{1} \right]\implies \underline{sin(x)}\left[\cfrac{1-sin^2(x)}{\underline{sin(x)}} \right] \\\\\\ 1-sin^2(x)\implies cos^2(x)[/tex]
recall again, sin²(θ) + cos²(θ) = 1.
