I have an equation:

$\displaystyle y = \frac{1}{\sqrt{1-2x^2+x^4+4x^2z^2}}$

$\displaystyle x, y$ is a variable and $\displaystyle z$ is a constant which we can vary. This equation produces peaks in graphs. I'm asked to find the maximum value of $\displaystyle z$ at which peak will be produced. Which mathematic method would I use? Can I have hints please. Thanks in advance.