`int cos(x) ln(sin(x)) dx` Evaluate the integral

You need to use the substitution `sin x = t,` such that:

`sin x = t => cos x dx = dt`

Replacing the variable, yields:

`int cos x*ln(sin x) dx = int ln t dt`

You need to use the integration by parts such that:

`int udv = uv - int vdu`

`u = ln t => du = (dt)/t`

`dv = 1 => v = t`

`int ln t dt = t*ln t - int t*(dt)/t`

`int ln t dt = t*ln t - int dt`

`int ln t dt = t*ln t - t + C`

Replacing back the variable, yields:

`int cos x*ln(sin x) dx = sin x*ln (sin x) -sin x+ C`

Hence, evaluating the integral, using substitution, then integration by parts, yields `int cos x*ln(sin x) dx = sin x*(ln (sin x) -1)+ C.`