# Help with pattern

• Mar 14th 2007, 04:08 PM
jacob23
Help with pattern
ax^3 + bx^2+cx+d=0 is standard form

How do I find the a, b, c, and d values given only a data table

Ex:
X | Y
0 | 0
1 | 3
2 | 14
3 | 39
4 | 84

What is the equation of that? it's cubic. What's the A B C and D?

Without using a calculator.

• Mar 14th 2007, 05:48 PM
topsquark
Quote:

Originally Posted by jacob23
ax^3 + bx^2+cx+d=0 is standard form

How do I find the a, b, c, and d values given only a data table

Ex:
X | Y
0 | 0
1 | 3
2 | 14
3 | 39
4 | 84

What is the equation of that? it's cubic. What's the A B C and D?

Without using a calculator.

y = ax^3 + bx^2+cx+d I suppose?

Plug the x and y values in.

So for (0, 0):
0 = a*0^3 + b*0^2+c*0+d
means d = 0

Now plug in the next point and the next point, etc. to get:
3= a + b + c
14 = 8a + 4b + 2c
39 = 27a + 9b + 3c

Now solve this system of equations.

-Dan
• Mar 14th 2007, 08:50 PM
jacob23
Thank you, that works and I knew that but that's not what I was looking for :( I'm looking for something like this
http://img300.imageshack.us/img300/3082/mathcopyof4.jpg
I want to be able to look at the table and determine the A B C D without having to do an equation. For the Quadratic pattern the A is the last column cut in half, the B is the top of the 1st column after Y minus the A. The C is the Y intercept.

How do you do I find the A B C D? please explain in detail.

Thanks again.:)
• Mar 15th 2007, 04:33 PM
jacob23