Question

Find the four second partial derivatives and evaluate each at the given point.
Function
f(x, y) = x^3 + 2xy^3 − 9y
Point
(9, 2)
fxx(9, 2) =

fxy(9, 2) =

fyx(9, 2) =

fyy(9, 2) =

Answer 1

Fx = 3x^2 + 2y^3
Fy = 6xy^2 - 9

Fxx = 6x
Fxy = 6y^2 = Fyx
Fyy = 12x

Now just plug in the numbers

Answer 2

do this just like the one above
for example
df/dx = 3 x^2 + 2 y^3
df/dy = 6 x y^2 - 9

d/dx (df/dx) = 6 x
etc