Hello again,
"katie deleted your answer to the question Hello,a=2, b=8, c=-1Indeed,y=f(x)=ax...
You've been warned"
Answer is a=2, b=8 and c=-1
Indeed:
y=f(x)=ax²+bx+c
Since (-2,-9) is the vertex,
y=k*(x+2)²-9
Or f(-1)=-7 ==> -7=k*(-1+2)²-9 ==> k=2
f(x)=2(x+2)²-9=2*(x²+4x+4)-9=2x²+8x+8-9
f(x)=2x²+8x-1
A proof: the picture is following.
