What is the quadratic function for (3,0), (-1,-12), (2,3)

Y = ax²+bx+c

Plug each pair in the above equation

for (3,0) → 0 = 9a + 3b + c

for (-1,-12) → - 12 = a - b + c

for (2, 3) → 3 = 4a + 2b + c

Solving this system of 3 variables will give you:

a = - 2

b = 7

c = - 3

Then the quadratic equation becomes:

y = - 2x² + 7x - 3