Respuesta :

Panoyin
X - Vertex
-8   = -8 = 4
2(-1)    -2

Y - Vertex
f(x) = -x² + 8x + 9
f(4) = -(4)² + 8(-4) + 9
f(4) = -(16) - 32 + 9
f(4) = -16 - 23
f(4) = -39

(x, f(x)) = (x, y) = (4, -39)