设f(x+y，xy)=x2+y2，则f(x，y)=()

设f(x+y，xy)=x2+y2，则f(x，y)=()
A、x2-2xy
B、y2-2x
C、y2-2xy
D、x2-2y
【正确答案】：D
【题目解析】：因为f(x+y，xy)=x2+y2=(x-y)2-2xy，故 f(x，y)=x2-2y，从而选D．