[tex]x(1,4,5)=4[/tex]
[tex]y(1,4,5)=100[/tex]
[tex]z_s=z_xx_s+z_yy_s=(4x^3+2xy)(1)+x^2(tu^2)[/tex]
[tex]z_s(1,4,5)=1,024,000[/tex]
[tex]z_t=z_xx_t+z_yy_t=(4x^3+2xy)(2)+x^2(su^2)[/tex]
[tex]z_t(1,4,5)=1,331,200[/tex]
[tex]z_u=z_xx_u+z_yy_u=(4x^3+2xy)(-1)+x^2(2st)[/tex]
[tex]z_u(1,4,5)=-450,560[/tex]
