Answer
(a) $(-1,-9)$
(b) $(-4,0),(2,0)$
(c) $(-2,-8),(0,-8)$
(d) see graph.
Work Step by Step
Given $f(x)=x^2+2x-8=(x+1)^2-9$, we have:
(a) the vertex is $(-1,-9)$
(b) for x-intercepts, solve $f(x)=0$ to get $(-4,0),(2,0)$
(c) for $f(x)=-8$, we have $x^2+2x-8=-8$, thus $x=-2,0$ or $(-2,-8),(0,-8)$
(d) see graph.
