Aloha :)
Wenn du den Integranden etwas umformst:$$f(x)=\frac{\cot(x)}{\sin(x)}=\frac{\frac{\cos x}{\sin x}}{\sin(x)}=\frac{\cos(x)}{\sin^2(x)}$$kannst du wegen \(\frac{d\sin(x)}{dx}=\cos(x)\) bzw. \(d\sin(x)=\cos(x)\,dx\) sofort integrieren:$$\int\frac{\cot(x)}{\sin(x)}\,dx=\int\frac{1}{\sin^2(x)}\,\cos(x)\,dx=\int\frac{1}{\sin^2(x)}\,d\sin(x)=-\frac{1}{\sin(x)}+\text{const}$$