What is symmetry?

Does the fraph of the function f (x) = x^(2) -3 have y - axis symmetry?

A disc of moment of inertia la is rotating in a horizontal plane about its symmetry axis with constant angular speed co. Another discinitially at rest of moment of inertia I, is dropped coaxially on to the rotating disc. Then, both the discs rotate with same constant angular speed The loss of kinetic energy due to friction in this process is,

What is radial symmetry?