Maximum and minimum values of curves and gradients

Question

Assignment:

For each of the following functions, find the maximum and mimimum values of the function on the circular disk: Do this by looking at the level curves and gradiants.

(A)  : f(x , y) = x + y + 3.
maximum value = 
minimum value =

(B)  : f(x , y) = 3x² + 4y²
maximum value = 
minimum value =

(C)  : f(x , y) = 3x² - 4y²
maximum value = 
minimum value = 

Provide complete and step by step solution for the question and show calculations and use formulas.