P9.38. Find the values of $I$ and $V$ for the circuits of
Figure P9.38, assuming that the diodes are
ideal. For part (b), consider $V_{in} = 0, 2, 6$, and
10 V. Also, for part (b) of the figure, plot $V$
versus $V_{in}$ for $V_{in}$ ranging from $-10$ V to 10 V.