+dfrac (sin npi )(n+dfrac {1)(n)}]
+dfrac (sin n)({2)^n} ;-|||-(2) _(n)=1+dfrac (1)({2)^2}+dfrac (1)({3)^2}+... +df
+dfrac (1)(n(n+1)) =-|||-(3) lim _(narrow infty )(dfrac (1)(2)+dfrac (3)({2)^2}+
+dfrac (1)((2n-1)(2n+1))]求极限
dfrac (1)(n-1)sum _(i=1)^n(({X)_(i)-overline (X))}^2 .-|||-n-|||-C. sqrt (dfrac
幂级数sum _(n=1)^infty dfrac ({(-1))^n}(2n-1)(x)^2n-1(|x|lt 1)的和函数sum _(n=1)^infty
+dfrac (1)({(2n-1))^2}(2n-1)x+... ] -|||-(B) dfrac (2)(pi )[ dfrac (1)({2)^2}sin
,求幂级数 sum _(n=1)^infty dfrac (2n-1)({2)^n}(x)^2n-2 的和函数,并求级数 sum _(n=1)^infty df
+dfrac (1)(sqrt {{n)^2+n}})=1
+dfrac (n)({n)^2+n+n})=dfrac (1)(2)证明: