Question

What is the vertex is of the graph of y=-2x^2+8x+9

Answer 1

Hi, 
$y=-2x^2+8x+9\\ =-2(x^2-4x+4-4)+9\\ =-2(x-2)^2+8+9\\ =-2(x-2)^2+17$

Vertex is (2,17)