### How to draw x^2-3*y^2=4 2d plot ?

It shows error, when I use 'y' variable, and says it is not defined.

So only plots of the form y=f(x) are allowed. How do I overcome this limitation in plotting?

And also how are 2d plots converted to 3D. I know how to do it. But how is it possible to make a 3d plot of a curve say, sin , as it is inherently in 2 dimensions.