Chapter 8 - Graphing Quadratic Functions - 8.4 - Graphing f(x) = a(x-h)^2 + k - Exercises - Page 446: 30

Vertex: $(-8,0)$

The quadratic function in the form $y=a(x-h)^2+k$ has the vertex $(h,k)$. $y=-(x+8)^2=-(x-(-8))^2+0$ It follows that $h=-8$, $k=0$. The vertex is: $$(h,k)=(-8,0).$$ The mistake is that $h$ is actually the $x$-coordinate of the vertex, not the $y$-coordinate. So it should be: $$(-8,0)$$