1. ## MAth Cubics

what is the cubic eqaution for the follwing coordinates
and how do i deduce it?
(1,10),(2,23)(3,38)(4,55)(5,74)(6,96)(7,120)(8,149 )

2. Hello, amak!

Are there typos in the problem?

What is the cubic eqaution for the follwing coordinates?

. . (1,10), (2,23), (3,38), (4,55), (5,74), (6,96), (7,120), (8,149)

There is no cubic that passes through these points!

In fact, the first five points lie on a parabola: .$\displaystyle f(x) \;=\;x^2 + 10x - 1$

. . and the other three points are quite "close" to the parabola.

3. Originally Posted by amak
what is the cubic eqaution for the follwing coordinates
and how do i deduce it?
(1,10),(2,23)(3,38)(4,55)(5,74)(6,96)(7,120)(8,149 )
You might try to use the equation:

$\displaystyle y=ax^3+bx^2+cx+d$

Pick 4 of your points, substitute them in 4 of these equations and solve the system for a, b, c, d.

Using (1, 10): $\displaystyle 10=a(1)^3+b(1)^2+c(1)+d$
Using (2, 23): $\displaystyle 23=a(2)^3+b(2)^2+c(2)+d$
.
.
...and so on.