Find the vertex of this parabola y=-x^2+6-8

Hello,

Your equation has a mistake: it is y=-x²+6x-8.

y=-x²+6x-8

= - (x²-6x) - 8

= - (x²-6x+9-9) - 8

= - (x-3) ²+9-8

= - (x-3) ²+1

Vertex is (3,1)

An other way more speedy:

y=-x²+6x-8

y'=-2x+6 = 0==>x=3 and y=-3²+6*3-8=1