Please clearly shows the steps. Thank you.

Let f : R2 - R be defined by f (x, y) = if ( x, y) + (0, 0), | 2 3 + ly|k if ( x, y) = (0, 0). (a) Show that f is continuous at the point (1, 2). (b) Let k = 3. Show that f is continuous at (0, 0). (c) Let k = 9. Determine, with justification, if f is continuous at (0, 0)