If f(x,y)=xy+(1/x)+(1/y) then f_xx?f_yy-f_xy² at (1,1) is

If r²=(x-a)²+(y-b)² then r_xx+r_yy=

If f(x,y)=x²Tan^-1(y/x)-y² Tan^-1(x/y),x≠0,y≠0 then f_xy=

If V is the volume of a rectangular box with edges x,y,z then V_xyz=

If f=x²yz+y²zx+z²xy then f_xyz=

If z(x,y) is the implicit function defined by x³+y³+z³=3xyz then xz_x+yz_y=

If u=3(lx+my+nz)²-(x²+y²+z²) and l²+m²+n²=1 then u_xx+u_yy+u_zz=

If Z=1n(1+x^r+y^r) then Z_xy=

If u=(x-y) (y-z) (z-x) then u_x+u_y+u_z=