Math Help?

I would suggest plugging each set of points in, resulting in 3 equations in terms of a, b, and c (a system of equations). Then, you can use Gaussian Elimination to make them row echelon form.

2 = a(1)^2 + b(1) + c
-18 = a(-3)^2 + b(-3) + c
-12 = a(3)^2 + b(3) + c

2 = a + b + c
-18 = 9a - 3b + c
-12 = 9a + 3b + c

eq 2 - eq 1
2= a + b + c
-20 = 8a - 4b
-12 = 9a + 3b + c

eq 3 - 3(eq 1)
2= a + b + c
-20 = 8a - 4b
-18 = 6a

a = -3
(plug a into eq 2) b = -1
(plug a and b into eq 1) c = 6

ANSWER: y = -3x^2 - x + 6

plug 3 points in ---> 3 equations , then solve for a , b , c