Question

I really need help with understanding this problem
Find a formula for the quadratic function with the points (2,0), (-1, 0), and (0,4)

Answer 1

so far what I have is 4a+2b+c = 0
a-b+c=0
c=4

-4a-2b-c=0
a-b+c=0
3(-3a-3b=4)

-a+b-c=0
c=4
-a+b=4

-9a-9b=12
-a+b=4
-10a-8b=16 but the b does not cancel out to give me a

Answer 2

@mathslover @dan815 @Hero @jim_thompson5910 @SolomonZelman

Answer 3

I set up three equations from the points and then I added equation 1 to equation 2 and equation 2 to equation 3.

Answer 4

y=ax^2+bx+c
c=4 from point (0,4)

a-b+4=0
b=a+4 from point(-1,0)

4a+2b+4=0
sub b=a+4
4a+2(a+4)+4=0
4a+2a+8+4=0
a=-12/6 = -2

and b=a+4 = -2+4 = 2
therfore
y=-2x^2+2b+4

Answer 5

what did you do in the second step?

Answer 6

which one

Answer 7

so I understand where you got the value for c
but a-b+4=0
b = a+4

Answer 8

are you just substituting the value of c in one of the equations?

Answer 9

and the 4a+2b+4 = 0
where is this from?

Answer 10

@dan815