2.利用逐项求导或逐项积分,求下列级数的和函数:-|||-(1) sum _(n=1)^infty n(x)^n-1 ;-|||-(2) sum _(n=1)^infty dfrac ({x)^4n+1}(4n+1) ;-|||-(3) +dfrac ({x)^3}(3)+dfrac ({x)^5}(5)+... +dfrac ({x)^2n-1}(2n-1)+... ;-|||-(4) sum _(n=1)^infty (n+2)(x)^n+3