Please compute this?

Question

Consider the function f(x, y)=y^2-x^2-yx^3.

Compute f(1, -1).

There's a triangle in front of f(1, -1), an opposite triangle.

Answer 1

Do you mean gradient? Here you go!

∇f(x, y) = ∂f/∂x i + ∂f/∂y j = (-2x-3yx^2)i + (2y-x^3)j

∇f(1, -1) = (-2+3)i + (-2-1)j = i - 3j <==Answer

Answer 2

Is there more to this problem?

If not then you can find f(1,-1) by just plugging in x = 1 and y = -1

f(1,-1) = -1^2 - 1^2 - (-1)(1^3)

f(1,-1) = 1