(int )_(0)^+infty x(2)^-xdx=( )(int )_(0)^+infty x(2)^-xdx=( )(int )_(0)^+infty x(2)^-xdx=( )(int )_(0)^+infty x(2)^-xdx=( )(int )_(0)^+infty x(2)^-xdx=( )

(int )_(0)^+infty (x)^3(e)^-2xdx= __

定积分(int )_(0)^3(2)^xdx=( ).A.(int )_(0)^3(2)^xdx=B.(int )_(0)^3(2)^xdx=C.(in

计算(int )_(0)^+infty dfrac (dx)({x)^2+4x+3}的值是A (int )_(0)^+infty dfrac (dx)({x)^

不定积分int (({e)^x+2)}^3(e)^xdx=()A、 int (({e)^x+2)}^3(e)^xdx=()B 、int (({e)^x+2)}^

(2) int x(e)^-xdx;

(int )_(-infty )^+infty (x)^2(e)^-a(x^2)dx=dfrac (1)(2)sqrt (dfrac {pi )({a)^3}}

()-|||-(2) (int )_(-infty )^+infty dfrac (2x)(1+{x)^2}dx=lim _(aarrow +infty )(i

7.计算下列定积分:-|||-(1) (int )_(0)^1x(e)^-xdx ;-|||-(2)(int )_(1)^xxln xdx;-|||-(3) (

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 )

5.设 _(1)=(int )_(0)^1xdx , _(2)=(int )_(0)^1sin xdx , _(3)=(int )_(0)^1tan xdx,