Find a non-linear function g r2 rarr r such that the

Question

Consider the two lines in the plane which are defined by the equations x + 2y = 2 and x + 2y = 4. Find the linear function f : R² → R such that the contour f(x, y) = 2 is the first line while the contour f(x, y) = 8 is the second line.

Find a non-linear function g : R² → R such that the contour g(x, y) = 2 is the first line while the contour g(x, y) = 8 is the second line.