4. Prove the following reduction formulas. x" dx 2 Vac + a 2an (a) In = In = In-1, n 21. at a 2n + 1 2n + 1 cos x sinn-1 x n - 1 (b) In = / sin" xdx; In = + In-2, n > 2. n n 1 (c) In = -n+1 - In-1, n >2. acn ( x + 1 ) dx; In = n+1 (d) In=/ x"sinxdx; In = " - n(n - 1)In-2, n > 2, then find 16