If $I_n=\int \sin ^n x dx $, then $n\; I_n-(n-1)I_{n-2}$=

Question

\[\begin {array} {1 1} (1)\;\sin ^{n-1} x \cos x & \quad (2)\;\cos ^{n-1} x \sin x \\ (3)\;-\sin ^{n-1}x \cos x & \quad (4)\;-\cos ^{n-1}x \sin x \end {array}\]