来自宋卫国的问题
设z=1xf(xy)+yϕ(x+y),f具有二阶偏导数,则∂2z∂x∂y=______.
设z=1xf(xy)+yϕ(x+y),f具有二阶偏导数,则∂2z∂x∂y=______.
1回答
2020-12-28 04:39
设z=1xf(xy)+yϕ(x+y),f具有二阶偏导数,则∂2z∂x∂y=______.
设z=1xf(xy)+yϕ(x+y),f具有二阶偏导数,则∂2z∂x∂y=______.
因为z=1xf(xy)+yΦ(x+y),所以,∂z∂y=1xf′(xy)•x+Φ(x+y)+yΦ′(x+y)=f′(xy)+Φ(x+y)+yΦ′(x+y),∂2z∂x∂y=∂∂x(∂z∂y)=yf″(xy)+Φ′(x+y)+yΦ″(x+y)=Φ′(x+y)+y(f″(xy)+Φ″...