Answer
(a) $-3,1$, (b) see graph below.
Work Step by Step
(a) List possible rational zeros as $\pm1,\pm3$.
Use synthetic division with these values and we can find three zeros as shown in the figure,
$x=1,1,1,$ and rewrite P as $P(x)=(x-1)^3(x^2+2x-3)$. Thus we find all the zeros
for the polynomial as $-3,1$.
(b) The graph of the function is shown in the figure.
