Answer
See graph and explanations.
Work Step by Step
(a) Given $f(x)=-2(x+3)^2-1$, we can identify its vertex as $(-3,-1)$, axis of symmetry as $x=-3$, domain $(-\infty,\infty)$, range $(-\infty,-1]$, increasing over $(-\infty,-3)$, decreasing over $(-3,\infty)$, see graph (red curve).
(b) Given $f(x)=2x^2-8x+3=2(x^2-4x+4)-5=2(x-2)^2-5$, we can identify its vertex as $(2,-5)$, axis of symmetry as $x=2$, domain $(-\infty,\infty)$, range $[-5,\infty)$, decreasing over $(-\infty,2)$, increasing over $(2,\infty)$, see graph (purple curve).
