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 )_(-infty )^+infty x(e)^-(x^2)dx;-|||-(3) (int )_(0)^+infty dfrac (1)(sqrt {{e)^x}}dx;-|||-(4) (int )_(1)^+infty dfrac (dx)({x)^2(1+x)};-|||-(5) (int )_(-infty )^+infty dfrac (dx)(4{x)^2+4x+5}-|||-(6) (int )_(0)^+infty (e)^-xsin xdx;-|||-(7) (int )_(-infty )^+infty (e)^xsin xdx;-|||-(8) (int )_(0)^+infty dfrac (dx)(sqrt {1+{x)^2}}