5. (a) (3 points} State the formal limit denition of the directional derivative. Explain each part. (b) (6 points} Explain the connection between the directional derivative, chain rule, and gradient. (c) [2 points} Consider the function f(:r,y) = $23,: + try-1. Compute the gradient of f. 1 (d) (3 points) Compute the directional derivative of f at the point (2,1) in the direction of if = E, E