設f(x)在[a,b]上連續(xù),在(a,b)內可導,證明:在(a,b)內至少存在一點ξ,使
A.yexy+2x/(x2+y2) B.xexy+2y/(x2+y2) C.yexy+(2x+2y)/(x2+y2) D.xyexy+2y/(x2+y2)