Question

How do you find a quadratic equation when given 3 points? My teacher taught us this weird data plot way, not completing the square.

Answer 1

I just copied some points from somewhere:
0.................. 5.8
1.................. 3.69
2.................. 2.16

Answer 2

use general equation : y = ax^2 +bx + c
then get 3 equations from 3 points to solve for a,b,c

5.8 = c
3.69 = a +b +c
2.16 = 4a +2b +c

substitute 5.8 for c into 2nd equation
3.69 = a+b+5.8
--> b = -2.11 -a
substitute into 3rd equation to solve for a
2.16 = 4a +2(-2.11 -a) + 5.8
2.16 = 2a +1.58
--> a = 0.29
--> b = -2.4
--> c = 5.8

y = 0.29x^2 -2.4x +5.8