graph of parabola

We know c is -1 cus c is the one that determines the y intercept. 

Plug in the coords of one of the dots adn subtract the two equations repeat till you get two equations with b and a u want to take away c cus we already know it.

2=3a+b

1=7a+b

4a=-1

a=-1/4

b=11/4

-1*-1/4*11/4=11/16

In vertex form

   y = a (x-3)^2 + 8       when x = 0   y = -1  (from the graph)

   -1 = a (9) + 8

  -9/9 = a = -1

 

-(x-3)^2 + 8 =   -x^2 + 6x -1         a = -1    b = 6    c = -1      take it from here.....