[m]=2x\cdot ln(x+y)+x^2\cdot\frac{(x+y)`_{x}}{x+y}=[/m]
[m]=2x\cdot ln(x+y)+x^2\cdot\frac{1}{x+y}[/m]
[m]\frac {∂^2z}{ ∂ x ∂y }=(z`_{x})`_{y}=(2x\cdot ln(x+y)+x^2\cdot\frac{1}{x+y})`_{y}=[/m]
[m]=2x\cdot\frac{1}{x+y}+x^2\cdot (-\frac{1}{(x+y)^2})[/m]
О т в е т.[m]\frac{∂^2z}{ ∂ x ∂y }=\frac{2x}{x+y}-\frac{x^2}{(x+y)^2}[/m]