Consider the function f(x, y, z)= x 2+ yz + z 2.(a) What is the gradient grad f of f, and what is its value at the point (2,3,1)?[3](b) What is the rate of change of f at the point (2,3,1) in the direction of the unit vector nb =33 i 33 j +33 k ?[2](c) What is the maximum rate of change of f at the point (2,3,1), and write down a unit vector that gives the direction that this maximum value occurs