Answer
See graph and explanations.
Work Step by Step
Step 1. Convert the equation into polar coordinates using $r^2=x^2+y^2, x=r\cdot cos\theta, y=r\cdot sin\theta$, we have $r^4=r^2cos^2\theta-r^2sin^2\theta$ which leads to $r^2=cos2\theta$ thus $r=\pm\sqrt {cos2\theta}$
Step 2. As the graph of $r=\sqrt {cos2\theta}$ is identical as $r=-\sqrt {cos2\theta}$, we graph the first one as shown in the figure.