L.5) Here's a plot of a certain surface z = f[x,y] over (and under) the rectangle R in the xy-plane consisting of all points {x, y, 0} with -1sxs 2 and -1sys 3 shown with a plot of R: X ab N o X 1 2 Why does the plot strongly suggest that Integrate[f [x, y], y, {x, R, ""}] > o How does the sign of f[x,y] tell you whether the surface plots out over R or under R