I'm trying to solve 

$$(yz,xz, xy) = (\lambda\frac{2x}{a^2},\lambda\frac{2y}{b^2},\lambda\frac{2z}{c^2})$$

with the constraint equation 

$$\dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}+\dfrac{z^2}{c^2}=1$$

What's the best way to proceed? I can't seem to first solve for $\lambda$.

Thanks,