Basic Mathematics - Old Questions

2. Define Gradient vector and directional derivative.[2+3+2+3]

Find the direction in which f(x, y) = 
(i) Increases and decreases most rapidly at the point (1,1).
(ii) What is the direction of zero change in f at (1,1)? 
(iii) Derivative of f(x, y) at the point (1,1) in the direction v = 3i - 4j.