设f有一阶连续的偏导数,且f(x+y,x-y)=4(x2-xy-y2),则xf'x(
题型:单项选择题
问题:
设f有一阶连续的偏导数,且f(x+y,x-y)=4(x2-xy-y2),则xf'x(z,y)+yf'y(x,y)为( )
A.2x2-8xy-2y2
B.-2x2+8xy-2y2
C.2x2-8xy+2y2
D.-2x2+8xy+2y2
设f有一阶连续的偏导数,且f(x+y,x-y)=4(x2-xy-y2),则xf'x(z,y)+yf'y(x,y)为( )
A.2x2-8xy-2y2
B.-2x2+8xy-2y2
C.2x2-8xy+2y2
D.-2x2+8xy+2y2