The parabola image passes through a (0,1) B (1,2) C (2, - 1), and the analytic expression of quadratic function is obtained

The parabola image passes through a (0,1) B (1,2) C (2, - 1), and the analytic expression of quadratic function is obtained

Let y = ax ^ 2 + BX + C (a ≠ 0). If the known image passes through a, B and C, then
0+0+c=1 (1)
a+b+c=2 (2)
4a+2b+c=-1 (3)
A = - 1, B = 2, C = 1
So, y = - x ^ 2 + 2x + 1