z=yf(xy,2x+y),f有二阶连续偏导数,求аz/аx,аz/аy,аz/аxаy
问题描述：
z=yf(xy,2x+y),f有二阶连续偏导数,求аz/аx,аz/аy,аz/аxаy
答
dz/dx=y(yf1'+2f2')
dz/dy=f(xy,2x+y)++y(xf1'+f2')
da/dxdy=(yf1'+2f2')+y【f1'+y(xf1'+f2')+2(xf1'+f2'）】
=2yf1'+xyf1';+2xf1'+4f2'+yf2谢谢你，里面的f1 ，f2是啥