積分怎麼積

method I

∫ cot x (csc x)^2 dx
= - ∫ csc x d(csc x)
= - (1/2) (csc x)^2 + C, where C is a constant

method II

Let u = csc x
du = - csc x cot x dx

∫ cot x (csc x)^2 dx
= - ∫ csc x (- csc x cot x dx)
= - ∫ u du
= - (1/2) u^2 + C
= - (1/2) (csc x)^2 + C, where C is a constant