Here's the question you clicked on:
Beatles
\[\int\limits \frac{\csc ^{2}(\frac{1}{x})}{x ^{2}}dx\]
let 1/x = u see what happens probably you get answer in cot
From what @experimentX said \(u = \frac{1}{x} = x^{-1}\) \(du = (-1)x^{-2} \ \ dx \ \rightarrow \ -du = x^{-2} \ \ dx\) See of you can find du hidden up there ;-)