Ok so i'm completely stuck on how to do this question i've been set for uni after just one very confusing and poorly delivered lecture...

Sketch Contours for the following functions, specifying the range of values allowed for z.

a) z^2 = [f(x,y)]^2 = 9 - 4x^2 - 4y^2

b) z^2 = [f(x,y)]^2 = 1 - 4x^2 - 9y^2

c) z^2 = [f(x,y)]^2 = 1 + 9x^2 - y^2

Any help or guidance on how to even get started on these would be fantastic! Thank you