We assume that y is a function of x, ie y=f(x)y=f(x) and then differentiate each side of the equation with respect to x, then re-arrange and solve for dy/dxdydx.
d/dx(x^3-3xy+2y^3)=d/dx(3)ddx(x3−3xy+2y3)=ddx(3)
therefore 3x^2-3xdy/dx-3y+6y^2dy/dx=0. (Used product rule and power rule)
therefore dy/dx(-3x+6y^2)=3y-3x^2. (Took out common factor)
therefore dy/dx=(3y-3x^2)/(6y^2-3x)
therefore dy/dx=(y-x^2)/(2y^2-x) (Divide all by 3).