Question

偏导数fxx fxy类题目怎么解 求解题过程

Answer 1

对某字母求偏导数，需要把其它字母看成常数 。
A、-4cos(2x+y)+sin(x-y)
B、-2cos(2x+y)-sin(x-y)
C、8sin(2x+y)+cos(x-y)
D、2sin(2x+y)+cos(x-y)
E、4sin(2x+y)-cos(x-y)
F、4sin(2x+y)-cos(x-y)

Answer 2

∂f/∂x=fx=-4cos(2x+y)+sin(x-y)
∂f/∂y=fy=-2cos(2x+y)-sin(x-y)
∂²f/∂x²=fxx=8sin(2x+y)+cos(x-y)
∂²f/∂y²=fyy=2sin(2x+y)+cos(x-y)
∂²f/∂x∂y=fxy(原题这里写错！)=4sin(2x+y)-cos(x-y)
∂²f/∂y∂x=fyx(原题这里写错！)=4sin(2x+y)-cos(x-y)