y = ax^2 + bx + 7 because when x = 0 y = 7
when x = -1 y = 14 so we have
14 = a - b + 7
so a - b = 7...............(1)
when x = 1 y = 4
so 4 = a + b + 7
a + b = -3.................(2)
Adding equations (1) and (2) we eliminate b so:-
2a = 4
a = 2
Substitute a = 2 in equation (1)
2 - b = 7
b = -5
so our equation is y = 2x^2 - 5x + 7
