Find the vertex of the graph of the equation y = -2x^2+8x-15 + 4x - 8.

This is what the parabola looks like when graphed (sorry for bad image quality), with a vertext at \(\color {red} 3, -5\)

y=-2x^2+12x-23

a=-2 b=12 c=-23

Use formula -b/2a: -12/-4=3

x=3

Plug in 3 as x: y=-2(3)^2+12(3)-23

y=-5

(3,-5)