Suppose that over a certain region of the xy-plane the electrical potential is given by V(x,y)=x^3-x^2y+y^2

a) Find the rate of change of the potential at P(-1, 1) in the direction of the vector u=<(3^1/2)/3,-(3^1/2)/3>

b) In what direction does V change most rapidly at P?

c) What is the maximum rate of change of V at P?

thanks