(dx^4)/(dx) = 4x^3
(d2y^2)/(dx) = (d2y^2)/(dy)*(dy)/(dx) = 4y(dy)/(dx)
(d (x^4+2y^2))/(dx) = (dx^4)/(dx)+(d2y^2)/(dx) = 4x^3+4y(dy)/(dx)
(d8)/(dx) = 0
Since x^4+2y^2=8
color(white)("XXX")(d(x^4+2y^2))/(dx) = (d8)/(dx)
color(white)("XXX")4x^3+4y(dy)/(dx)=0
color(white)("XXX")4y(dy)/(dx) = -4x^3
color(white)("XXX")(dy)/(dx) = (-4x^3)/(4y)=-x^3/y