What is the vertex of the function f(x)=x2-8x-9

Mr and mrs smith buy tickets for themselves and their four children. the cost of an adult ticket is ? 6 more than the adult ticket. the total cost of the six tickets is ? 40.50 work out the cost of an adult ticket. in your working let c be the cost of the child ticket and a be the cost of the adult ticket.

The center of the circumscribed circle lies on line segment and the longest side of the triangle is equal to the of the circle.

Find the equation using the point (4,8)