Question 103792
vertex=(h,k)=(h,17)
-(x-h)^2+17=-x^2+bx+8
We need a -9 to add to 17 to give 8. a has to be negative to give -x^2. h must be negative so that the vertex can be in the 2nd quadrant. 
h=-3
-(x+3)^2=-(x^2+6x+9)+17 
=-x^2-6x-9+17
=-x^2-6x+8
b=-6 Ans.
Ed
{{{graph(500,500,-10,10,-1,19,-x^2-6x+8)}}}