This is the full question but i need help with all b

6) [35] For the smooth function f that satisfies: of of 1,2 =9 1,2 =5 1,2 =7 f ( ) ax( ) ay( ) (a). Write the linear approximation of f (x, y) centered at (1,2). (a'). Write an equation of the tangent plane to z = f (x, y) at (1,2,9) . (a"). Write an equation of the tangent line to 9 = f (x, y) at (1,2) . (b). Compute: %(Lf(l,2)[1+(vlJW)I)2+(VZJW)I)) (b'). Compute the rate of change of f (x, y) at (1,2) in the direction of (121,122 ). (1)"). 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