Question 204619: I need to find a quadratic equation for the following table
x y
0 0
2.2 30
2.9 40
4.0 50
5.0 60
6.5 70
8.0 80
9.0 90
11.8 100
This is an excel problem. but i dont know how to make excel do a quadratic equation. Answer by ankor@dixie-net.com(22740) (Show Source):
You can put this solution on YOUR website! I need to find a quadratic equation for the following table
x y
0 0
2.2 30
2.9 40
4.0 50
5.0 60
6.5 70
8.0 80
9.0 90
11.8 100
:
using the form y = ax^2 + bx + c
x=0, y=0, tells us that c = 0
:
Use two coordinates to find a & b
x = 4, y = 50
x = 9, y = 90
:
x = 4
16a + 4b = 50
:
x = 9
81a + 9b = 90
:
use elimination, mult the 1st equation by 9, the 2nd equation by 4:
144a + 36b = 450
324a + 36b = 360
------------------ subtraction eliminates b
-180a = 90
a =
a = -.5
find b using the 1st equation
16(-.5) + 4b = 50
-8 + 4b = 50
4b = 50 + 8
4b = 58
b =
b = 14.5
:
The equation:
y = -.5x^2 + 14.5x
:
The graph
:
This satifys the data approximately; actual values in brackets:
x y
0 0
2.2 30 (29.5)
2.9 40 (37.8)
4.0 50 (50)
5.0 60 (60)
6.5 70 (73)
8.0 80 (84)
9.0 90 (90)
11.8 100 (101.5
