Відповідь:

Покрокове пояснення:

[tex]\frac{d^2z}{dx^2}:\\[/tex]

[tex]\frac{dz}{dx} =-2cos(x+y)sin(x+y)[/tex]

[tex]\frac{d^2z}{dx^2}=-2*(-sin(x+y))*sin(x+y)+(-2*cos(x+y)*cos(x+y))=\\\\=-2(cos^2(x+y)-sin^2(x+y))=-2cos(2x+2y)[/tex]

[tex]\frac{d^2z}{dxdy}:\\[/tex]

[tex]\frac{dz}{dx} =-2cos(x+y)sin(x+y)[/tex]

[tex]\frac{d^2z}{dxdy}=-2*(-sin(x+y))*sin(x+y)+(-2*cos(x+y)*cos(x+y))=\\\\=-2(cos^2(x+y)-sin^2(x+y))=-2cos(2x+2y)[/tex]