# Thread: Finding equation of a cubic function?

1. ## Finding equation of a cubic function?

How do you do find the equation of a cubic function?

2. Originally Posted by llamajuice
How do you do find the equation of a cubic function?
find what ... zeros?

http://www.mathhelpforum.com/math-he...functions.html

3. theres no zeroes.
like its just a normal graph and i need to find an equation that models the behavior of the graph.

4. Originally Posted by llamajuice
theres no zeroes.
like its just a normal graph and i need to find an equation that models the behavior of the graph.
... how do you know the data models a cubic equation?

5. because it looks like one.
well first i just plotted the points into excel then i tried all the lines of best fit to see which one it matched. It could also be a sine graph thing, but any polynomial of a degree of 3 or higher works too so i thought finding a cubic function that matches it would be easiest.
do i just sub in points into y=ax^3 +bx^2 +cx +d to get 4 formulas then solve?

6. Originally Posted by llamajuice
because it looks like one.
well first i just plotted the points into excel then i tried all the lines of best fit to see which one it matched. It could also be a sine graph thing, but any polynomial of a degree of 3 or higher works too so i thought finding a cubic function that matches it would be easiest.
do i just sub in points into y=ax^3 +bx^2 +cx +d to get 4 formulas then solve?
give it a go ... I cannot make a judgement w/o knowing how the data originated.

7. its like height vs age so theres no x- intercepts

8. Originally Posted by llamajuice
its like height vs age so theres no x- intercepts
Height vs age is likely to be linear since there's a direct correlation. Best thing to do is plot in excel and guess the best fit

9. scratch that its body mass index