Table:
x y
-3 0.5
-2 1
-1 2.5
0 5
1 8.5
Now, y = ax^2 + bx + c
Start replacing x = 0 and y = 5
5 = a(0) + b(0) + c => c = 5.
Now, replace any other two pair of data:
(-2, 1) => -1 = a(-2)^2 + b(-2)
-1 = 4a - 2b
(1, 8.5) => 8.5 = a(1)^2 + b(1)
8.5 = a + b
Solve the system
4a - 2b = - 1
a + b = 8.5
=>
4a - 2b = - 1
2a + 2b = 17
-------------------------
6a = 16
=> a = 16 / 6 = 8/3
b = 8.5 - a = 17/2 - 8/3 = 35/6
=> y = (8/3)x^2 + (35/6)x + 5 <--------- answer
