九、(7分)设f(x,y)在 ^2+(y)^2leqslant 1 上二次连续可微,且满足 dfrac ({partial )^2f}(partial {x)^2}+dfrac ({partial )^2f}(partial {y)^2}=(e)^-((x^2+{y)^2)},-|||-试求 iint (xdfrac (partial f)(partial x)+ydfrac (partial f)(partial y))dxdy.