cosl×tgl/sin²l-ctgl×cosl=sinl

cosl*\frac{tgl}{sin^2l}-ctgl*cosl=sinl\\ \\\frac{cosl*\frac{sinl}{cosl}}{sin^2l}-\frac{cosl}{sinl}*cosl=sinl\\\\\frac{1}{sinl}-\frac{cos^2l}{sinl}=sinl\\\\\frac{1-cos^2l}{sinl}=sinl\\\\\frac{sin^2l}{sinl}=sinl\\\\sinl=sinl\\\\P.s \,\, sin^2l+cos^2l=1