For the function f(x,y)=3x^2+6y^2+8/(9x^2-36y^2)
a) Enter the coordinates of a point in the domain of f(x,y)?
b) Enter the coordinates of a point not in the domain of f(x,y),with positive x-value?
c) Enter the coordinates of a point not in the domain of f(x,y)with negative x-value?