9. Let f(x,y)=x^4 y^2+ y and P=(1,2). Find the unit vector that points in the direction of maximum rate of increase at P. Find the rate of change in the direction A=(2,1).

10. Let f(x,y)=x^2+xy+y^2. What is the direction in which f is increasing the most rapidly at the point (1,1) ? Find the directional derivative of f in this direction.