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How to factor

How to factor
Does the sight of a number or expression accompanied by the instructions, "Factor completely," strike fear into your heart? Wish you paid attention in algebra? Well, this instructable will teach you how to factor any number, or eligible expression such as Ax^2 + Bx + C.
 
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Step 1Factoring numbers

Factoring numbers
First off, what is a factor?

"Natural number factors" are the complete set of whole numbers, where if you multiply one number in the set by another in the set, you get the number that you're factoring.

For example, the number 5 has two factors: 1, and 5. The number 6 has four factors: 1, 2, 3, and 6.

"Integer factors" include negative numbers.

The number 5 in this case would have four factors: -5, -1, 1, and 5. 6 would have eight factors: -6, -3, -2, -1, 1, 2, 3, and 6.

(Natural numbers are numbers without fractions, starting from 1, 2, 3, 4, 5... all the way up to infinity. Integers are natural numbers, as well as their negative counterparts and 0, or ...-5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5...)

Factoring numbers with the natural number set is simple. Every number has at least two factors. To find other factors, start dividing the number starting from two and working your way up until you reach that number divided by 2. Any quotient that does not have a remainder means that both the divisor and the quotient are factors of that number.

Say you need to factor the number 9. You can't divide by two evenly, so we skip it. (Note the solution, 4.5, so you know when to stop later on.) 9 is divisible by 3, so add 3 to your list of factors. Work your way up until you divide by 5 (9 divided by 2, rounded up). You'll end up with 1, 3, and 9 as a list of factors.

When factoring numbers in the integer set, you can just add the negative equivalent of your solutions from natural number factoring in. So 9 would have factors of -9, -3, -1, 1, 3, and 9.

Factoring negative numbers can only be done with integer factoring. The solution is the same one you get factoring the positive version of the number. -9 has factors of -9, -3, -1, 1, 3, and 9.

Zero is the only integer that has an infinite amount of factors, and is the only one that has zero as a factor.
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45 comments
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Mar 7, 2012. 8:44 PM!!!Jenna!!! says:
I don't understand how to simplify radical expressions. The whole Factor, Seperate, Simplify thing confuses me. I get most of it except how they factor and where they get all the random numbers from. I guess I just don't understand how to factor. For example, one of the questions was :...........

3(cube root) and then the radical sign and then 24n^2 x 3(cube root) and then the radical sign and then 36n^2..............

sorry i don't know how to make it look like the actual problem! How would I factor and solve that? Because obviously i am too dumb to figure it out on my own. online school is hard for me.
Jan 2, 2012. 3:06 PMbseibert says:
Kumon's Math Study Guide provides this question:

Know how to "factor" Binomials:
Problem: -3x^2 + 7x
Answer: 0, 7/3

I thought the obvious answer is pulling out the x for the original binominal which would result in x (-3x+7)

Although I haven't seen this before, I could take each of the factors and have them equal 0 to come up with the answer. Am I missing something?

Example: x = 0 and -3x + 7 = 0
Solve for x, x = 0 and x = 7/3
Dec 4, 2011. 4:16 PMpopewill says:
Oh no. I hate factoring and FOILing with a passion. I thought it was the weekend but i guess you can never escape math :/.
Jan 14, 2011. 7:39 PMmogg says:
(2x^2 +5x^7) (1+3x) ->
x^2(2+5x^5)(1+3x)

Answer has 3 factors (^^)
Jan 6, 2011. 2:24 PMneomancer45 says:
This instructable and all possible future ones would be easier to read if you used the conventional sign indicating a power, the carrot. (^)

2x2 is strange looking, and could b thought of as 2 times x times 2

also, this gets more complicated when u have variable powers, as x to the power of y, which is different when written as xy.

ex:
x to the power of 4
wrong:
x4
right:
x^4
Sep 27, 2010. 5:10 AMilovetine says:
can you please give an example of factoring binomials ?
Sep 4, 2009. 6:46 PMMattonator says:
In the binomials section he tries to explain how to factorise 2x2-4x, to get to the answer 2x(x-2). He did this by expanding the binomial function. The common factor in the equation 2x2-4x is 2x, this is because there is a 2x in 2x2 obviously but a 2x inside -4x also. therefore if you times 2x(x-2) out you will get 2x2-4x. This is because 2x times x = 2x2 which is the first part of the equation and 2x times -2 gives the answer -4x because a positive times a negative is a negative number.

Hope this explains it, if not, reply to me
Jan 13, 2010. 11:23 AMSaltyseaman says:
factor, not factorise. you just failed at trying to look smart.
Sep 13, 2009. 9:08 AMladams234 says:
Need more explanation, please. For example, how would you factor 4v squared - 81t squared. I cannot figure it out from the instructable above, or yours. HELP!
Sep 13, 2009. 2:24 PMladams234 says:
Thanks! I did some research and found the same answer you did. I just wasn't quite understanding it before - thanks again!
Sep 3, 2009. 12:37 PMMister nobodie says:
Rated 0.5 (worthless). And thats really what this is. You didn't even explain how you got to 2x (x - 2) for the binomials section. This is pretty much what you did: HOW TO FACTOR 1) factor problem 2) get answer.
Jan 13, 2010. 11:23 AMSaltyseaman says:
Nerd rage.
Dec 2, 2009. 1:19 PMbassclarinet23 says:
My teacher gave us a song to memorize the Quadratic Equation...

(Imagine the tune of "Pop! Goes the Weasel".)

The opposite of lower case "B",
Plus or minus the square root,
Of "B" squared minus 4(ac),
All over 2a.

Fin.

It's irritating, but you'll remember the formula.


Pronounce...
4(ac) = four "A" "C"
2a = two "A"

Dec 2, 2009. 5:27 PMbassclarinet23 says:
Ha ha. Cool.
Nov 8, 2008. 5:34 AMmi9d says:
Sorry, but shouldn't n=3.x.x ?
I mean 9.x.x times 9.x.x = 81.x.x.x.x

( sorry, can't type the power superscripts )
Sep 4, 2009. 6:55 PMMattonator says:
9x2 times 9x2 is 81 * 81 which = 6561 which is the same as 9*9*9*9 or 94.

814 is 43,046,721
May 8, 2009. 11:56 AMShinta786 says:
oh man, I just scrolled to the comments in 5secs. don't dare to read this, but must be good
Oct 27, 2008. 3:56 PMmad rabid sh33p says:
I hate factoring lol - we have to do this huge 125 Q. packet for Algebra II. If I need help, I'll be sure to reference this. ;D
Oct 12, 2008. 1:27 AMBlazo says:
This is a good instructable and i dont know about you but we learned this in 7th grade. By the way im from Macedonia and at 7th grade kids are usualy 12-13 yrs old. :D
Oct 3, 2008. 9:56 PMmenace says:
How about factoring polynomials?
ax4+bx3+cx2+dx+e
synthetic division
normal division those would be reallly helpful.
Sep 28, 2008. 8:41 PMjosefu0 says:
omg this schooling is boring.
Sep 26, 2008. 6:19 AMHeyarnold says:
FOIL ftw! brings back memories of my math tutoring days.
Sep 22, 2008. 11:45 PMcodz30 says:
HP 39gs -> POLYROOT
Sep 23, 2008. 12:18 PMundeadbydawn says:
this is a really nice, deep and informed feature... except in that you use the word 'factor' four times in explaining what a factor is. So unless you already know what a factor is the explanation isn't going to make sense. 1st rule of explanation: assume your student knows nothing. Otherwise, math tutorials are a Damned Fine Plan, please do keep 'em coming :-)
Sep 23, 2008. 4:50 PMundeadbydawn says:
Happy to help. It is a superb feature either way.
Sep 22, 2008. 3:04 PMBurning Questions says:
(removed by author or community request)
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