Chapter 9 - Conic Sections, Sequences, and Series - 9.1 Parabolas and Circles - 9.1 Exercises - Page 700: 5

$a=-\frac{1}{2}$ and so the parabola opens left $h=4$ and $k=0$ and so the vertex is $(4,0)$. Since the parabola opens left, the axis of symmetry is $y=0$.

$x=-\frac{1}{2}y^2+4$ $a=-\frac{1}{2}$ and so the parabola opens left $h=4$ and $k=0$ and so the vertex is $(4,0)$. Since the parabola opens left, the axis of symmetry is $y=0$.