_________.
_________.
B: (Xgt X)=(int )_(-infty )^xf(x)dx-|||-C: (int )_(-infty )^+infty f(x)dx=1 D: (
(int )_(-infty )^+infty (x)^2(e)^-a(x^2)dx=dfrac (1)(2)sqrt (dfrac {pi )({a)^3}}
(int )_(0)^+infty dfrac (x{e)^-x}({(1+{e)^-x)}^2}dx= ()-|||-__
1.讨论下列无穷积分是否收敛?若收敛,则求其值:-|||-(1) (int )_(0)^+infty x(e)^-(x^2)dx;-|||-(2) (int )
()-|||-(2) (int )_(-infty )^+infty dfrac (2x)(1+{x)^2}dx=lim _(aarrow +infty )(i
(int )_(e)^+infty dfrac (dx)(x{ln )^2x}= __
[例3] (int )_(0)^+infty dfrac (x{e)^-x}({(1+{e)^-x)}^2}dx
(int )_(-infty )^+infty dfrac (dx)({x)^2+2x+2}..
4.下列结论正确的是 ()-|||-(A) (int )_(-infty )^+infty dfrac (x)(1+{x)^2}dx=0 (B) (int )_
(2)int_(-infty)^+infty(dx)/(x^2)+2x+2;(2)$\int_{-\infty}^{+\infty}\frac{dx}{x^{2