Please help me slove this question.

\f(b). Compute: 2 ( L , (1 , 2) ( 1 + ( 1 , / V (V, ) 2 + ( V2) ? ) 1,2 + ( 12 / V (V,)= + (V2 )? ) 1 ) (b'). Compute the rate of change of f(x, y) at (1,2) in the direction of ( v, V2 ) . (b"). Explain why your answer in (b') and (b") are the same. (b""). Write your answer in (b') as the product of the magnitude of some vectors and the cosine of the angle between two vectors