The boundary of D, the line from (0,0,1) to (2,4,0), is shown in part (b) of the figure as a dashed line; it has equation y=2x. (We can recognize this in two ways: one, in collapsing t...The boundary of D, the line from (0,0,1) to (2,4,0), is shown in part (b) of the figure as a dashed line; it has equation y=2x. (We can recognize this in two ways: one, in collapsing the line from (0,0,1) to (2,4,0) onto the x-y plane, we simply ignore the z-values, meaning the line now goes from (0,0) to (2,4).
