(3 points) Let $f(x, y) = 1 - xy^2 - yx^2$. Compute the cartesian equation of the tangent plane to $f(x, y)$ at the point $(0, 0)$.
(2 points) Let $f(x, y) = xe^y$. Draw the graphs of $f(2, y)$ and $f(x, 2)$.
(1 point) Write the parametric equation of the sphere with center in $(0, 0, 0)$ and radius 1.