So, you have a geek girlfriend or want to impress some geek girl. You can try following tip or I should say inadvertent Google easter egg.
Its pretty simple, just ask her to search following string on Google:
(sqrt(cos(x))*cos(200x)+sqrt(abs(x))-0.7)*(4-x*x)^0.01, sqrt(9-x^2), -sqrt(9-x^2) from -4.5 to 4.5
For impatient or lazy, curious dudes here is a shortcut link to this Google Graph Trick.