question about factoring x^3's

[skim milk]

i never got this down

factoring equations that have x^3 in it

for example, x^3+5x-7 or whatever, how do i factor that out?

i only have a ti-83 btw, no ti-89 :[

can someone please explain it to me? use equation you wish as long as "x" is cubed thanks

 

[tweakmm]

x^2 * x =???

 

[skim milk]

it would look something like (x-1)(x^2+5x-5) <--- just an exmaple
that would be how the factor will look like

i'm asking how to get that answer though

 

[tweakmm]

Originally posted by: fritolays
i'm asking how to get that answer though

it seems like you know how to get the answer
do you want somebody to do the work for you and tell you the answer?

 

[Shooters]

I forgot exactly how to do it by hand. If I remember correctly, it's kind of a trial and error process, unless you're a math wiz and the solution is obvious to you. Do a search on google for factoring a cubic polynomial and you'll find it.

Or you could just do what I do.....graph the equation on your calculator and find the three roots.

Edit:
This explains it.

 

[speg]

Yeah but good look finding a value for x that you can equal zero, I can't seem to find a simple one

 

[Shooters]

Originally posted by: speg
Yeah but good look finding a value for x that you can equal zero, I can't seem to find a simple one

That's why I would use a calculator to do it.

 

[dighn]

or use the cubic formual!!

LOOLOL

http://www.math.vanderbilt.edu/~schectex/courses/cubic/

 

[Syringer]

If it's x^3 + 5x - 7, you can just look at it and see that if you x = 1, you get 0. That means that x=1 is a factor, so you divide the function by x-1..in which case you'd use synthetic division.

 

[speg]

Umm, 1+5-7=-1...

 

[dighn]

Originally posted by: Syringer
If it's x^3 + 5x - 7, you can just look at it and see that if you x = 1, you get 0. That means that x=1 is a factor, so you divide the function by x-1..in which case you'd use synthetic division.

no man at x = 1, u get -1

 

[Dudd]

I'd use my calc, or use De Moivre's Theorem coupled with the Rational Root Theorem along with synthetic division. I can't remember exactly what all those things are, as we learned them in Pre-Calc and never used them in Calc I, but I seem to remember that they are the stuff you want to be looking at.

 

[skim milk]

Originally posted by: Dudd
I'd use my calc, or use De Moivre's Theorem coupled with the Rational Root Theorem along with synthetic division. I can't remember exactly what all those things are, as we learned them in Pre-Calc and never used them in Calc I, but I seem to remember that they are the stuff you want to be looking at.

i have a ti-83 plus
how do i factor it out with my calculator?

 

[Shooters]

I have a TI-86, so I'm not sure if it's the same on the 83 but it's probably similar. Look for the poly function, then just punch in the order of the polynomial (3 in your case) and then the coefficients.

 

[Dudd]

Originally posted by: fritolays

Originally posted by: Dudd
I'd use my calc, or use De Moivre's Theorem coupled with the Rational Root Theorem along with synthetic division. I can't remember exactly what all those things are, as we learned them in Pre-Calc and never used them in Calc I, but I seem to remember that they are the stuff you want to be looking at.

i have a ti-83 plus
how do i factor it out with my calculator?

Find the root (there has to be at least one), and then use synthetic division to get it down to a second degree equation.

 

[Syringer]

Originally posted by: dighn

Originally posted by: Syringer
If it's x^3 + 5x - 7, you can just look at it and see that if you x = 1, you get 0. That means that x=1 is a factor, so you divide the function by x-1..in which case you'd use synthetic division.

no man at x = 1, u get -1

Eck, so it is.

Is that function correct? When you solve for x you get 1.1194..

 

[DanFungus]

Originally posted by: Dudd

Originally posted by: fritolays

Originally posted by: Dudd
I'd use my calc, or use De Moivre's Theorem coupled with the Rational Root Theorem along with synthetic division. I can't remember exactly what all those things are, as we learned them in Pre-Calc and never used them in Calc I, but I seem to remember that they are the stuff you want to be looking at.

i have a ti-83 plus
how do i factor it out with my calculator?

Find the root (there has to be at least one), and then use synthetic division to get it down to a second degree equation.

after the teacher makes you use long division for these kinds of problems, you learn to love synthetic division when the teacher teaches it to you

 

[ddjkdg]

Since someone said the solution is not a whole number you can't factor this equation. You wouldn't get it on a test. But if do do get a factorable equation here's what to do: Either graph it to find an integer solution, or guess (the only possible integer solutions will be factors of the constant in the equation). Then use synthetic division and take that part out of the cubic. This will leave you with a quadratic which you know how to solve (hopefully).

 

[pookguy88]

we've come down to using calculators to factor now..... how sad is that. pretty soon we'll be using calculators to add fractions... wait....