## Calculus (3rd Edition)

The equation $$4z=9x^2+5y^2$$ can be rewritten as follows $$z=\left(\frac{x}{2/3}\right)^{2}+\left(\frac{y}{1/\sqrt{3}}\right)^{2}$$ which is an equation of an elliptic paraboloid with $a=2/3, b=1/\sqrt{3}$ (see equations on page 691).