# Dedicated to Comrade Otto Bretscher.

Calculus Level 5

Let $$S$$ be the surface: $z=x(1-x)y(1-y)$

Such that

$$0\leq x,y\leq 1$$

Evaluate the integral:

$\int \int_{S} x\mathbf{k}.d\mathbf{A}$ where $$d\mathbf{A}$$ is the upward-pointing normal vector.

×