Solving a quadratic by factoring

[KswolfVideos]

I've been trying to learn how to factor for several weeks.

I just learned how in nine minutes.

[WhatTheShizzzzz]

better than my teacher

[morenojader]

okay if X=-2 and X=-4 why the parabola is on the right side???

[MegaLance77]

my algebra 2 teacher is a poser. YOU ARE MY MATH TEACHER!!

[capsc415]

little kid: MOMMY! Can i go beat up 8 people?

mom: DEPENDS... whose on your side?

little kid: I have 127 people on my side...

mom: why do you wanna beat up these people?

little kid: BECAUSE THEY DISLIKED AN INGENIOUS VIDEO. *shows this khan academy video*

mom: if you told me that in the first time you could beat those people up ANYTIME you want!

THE END

[Theshooter7]

Wow. All these years, through high school and everything, I never understood factoring because they constantly explained it in an overly complicated manner. But this video actually made it all easy to understand. Amazing job, thank you!

[Glamerth]

119,820 Views......8 dislikes. HECK YES. =D

[DeptBookDave]

Nevermind. Just noticed that my equation had a coeffecient on the x^2 term. Sorry for wasting comment space with my oversight.

[DeptBookDave]

I'm sure this is going to sound extremely foolish, but does anyone know any way to factor a quadratic with a 1 as the constant? Its status as the only single-factor number seems to mess up this process.

[vadimasPK]

im using discriminant formula its more simpler

[jzizzlely]

slide and divide?

[lpoiuy341]

There is a book that only works with Algebra. I use this book while learning from this amazing teacher. It's called Effortless Algebra. This book shows step by step how to do algebra. I suggest to you all to get this book. It helps me a lot.

[soopi49]

Thanks very much Khan, this is really great and easy to follow.

[RollsRoyceMr]

the zeros are -2, -4 but your graph is showing 2, 4 or is it your concept of cartesian plane that is wrong ?!?!

[valdas0]

@RollsRoyceMr yes, his graph is wrong. Parabola should cross the x-axis at -2 and -4.

[McYellowfish]

@bolmung He just drew it to show you what it looks like. He says he doesn't know the actual size.

[Equifish]

I use a similar method, but could someone tell me if it is right?:

(1)Let inequality become and equal sign.

(2)Solve as a standard quadratic equation

(3)Plot x solutions on x axis without ranges

(4)Test ranges around points by substituting numbers on the x plane to see if it fits the original in-equation

Is this correct?

Thanks,

[bolmung]

=(

Was that parabola he drew in the beginning for the first problem just an example of what a parabola looks like? Because he got negative answers....

Would they have intersected the x axis on the negative side?

Or am I not getting something? >.<

[234234234mr]

@bolmung that was just an example of what one looks like in the beginning.

[1ceMasterr]

@basalduat

that is a mistake as he made the graph before he continued to solve the equation.

[MadkeenJohn]

Your videos are FANTASTIC IF you have no clue about anything to do with the subject. But very tedious for someone who is using your videos as a 'revision' tool as i am.

BRILLIANT Video's and they will certainly help me pass my C2 maths exam next week!! :D

[XxXCrOuChXxX]

Thank you !! Now i know how to solve correctly :D

[basalduat]

x= -4 and x= -2 is correct but your drawing shows that x=2 and x =4 ???

[RollsRoyceMr]

ye, kid khan doesn't know math, ...i guess that explains why he ditched Math later to get Masters in EECS, easy way out.

[Gakupo777]

Wow! This is really helpful!!! Thanks for putting this up!!!

[MixesAndStuff]

Sal, this video is out of place in the playlist because you haven't defined function and parabola yet.

[CutieTheGP]

i love u

[mathmatchpoint]

If you want to become good at Mathematics go to my channel: ( Mathmatchpoint ). In my videos I'm going to teach you Math the easy way. I'll teach you all Math topics; from the basic to the advanced topics. I promise that you will become good at Math if you watch my videos and do the provided exercises. You can watch my Math videos in order by clicking on Playlists.

[MovieMad007]

god if only I had this when i was at school I'd have been the top of the class!! Am 38 now and did my GCSE in summer of 86! The books that are around now like the "Dummies" series - eeesh I only wish I had these back then!

[Jokerk1d]

erm...whats he talkin about ? what video should i watch before this?

[charliee53]

@Jokerk1d i know rite?!?

[LancerZEV]

This video is should be further in the list because you haven't explained the concepts of fuction and parabola.

[marsunderscorefenix]

@LancerZEV well, he took up the most of the 10 mins allowed, i dont see how he could have fit it in there, he's down a good job

[marsunderscorefenix]

@LancerZEV wooow, sorry, I didn't know that you were the grammar.

[marsunderscorefenix]

@LancerZEV wooow, sorry I didn't know that you were the grammar police

[marsunderscorefenix]

@LancerZEV I didn't realize that missing one letter would cause you to "decipher" it... I think it's pretty obvious what I meant.

[marsunderscorefenix]

@LancerZEV deal with it

[iWriteUinMyDeathNote]

@LancerZEV @MixesAndStuff

what videos do you first have to watch to understand this? i already watched the function videos but i still don't get it

[THEBASEBALLRAMBO]

... ill trade you brains ..

[idster7]

is there any way to get the answers algebraically starting with A+B=-1 and AxB=-30??

[Joe62530]

The graph you sketched for the first function is incorrect, it should cross the x-axis at -2 & -4, not at 2 & 4.

[furyofnasa]

@Joe62530 Yes I agree ;P But oh well

[TheMangoGuy]

@Joe62530 He clearly stated he doesn't exactly know what it's going to look like, he just gave a generalization of what it could look like

[MinaretsHacker]

@badmintonplayer08 No x should equal negative five.

[MinaretsHacker]

This is my homework and I can't hear you, I have to hold the speaker up to my ear with everything all the way up, so could you please speak louder in future videos?

[printing11]

hes speaking fine....

[MinaretsHacker]

No it's my stupid speakers. I was using my desktop and it has horrible speakers that barely work.

[23davidbeckham07]

wear a headphone u idiot !!

[Zegorn]

No, not idiot, he probably didn't think of it... But yeah, just where ear buds or head sets... etc...

[mrhnm]

When i factored it I got (2x+10)(x+5) can that work?

[hotcopone]

hi thanks for the video. it really helps.. 1 thing tho. i recommend u should get those digital pen mouse things. its alot easier to write with and makes it alot clearer. thanks anyway... :)

[badmintonplayer08]

at the very end of the video isn't it suppossed to be

x= -6 0r x= 5......why did he put 5 as a negative?

[nkolatsis]

His mistake I would think. -6 +5 = -1 which +6 -5 does not equal.

[NeoXC]

All you need to do is plug in the coefficients into the quadratic formula:

(+/- is plus or minus)

x = (-B +/- sqrt B^2 - 2AC) / 2A

The coefficients in x^2-5x-3 are:

A=1

B=-5

C=-3

Plug those back into the quadratic formula and you'll end up with 2 results for x.

x = (5 + sqrt 31) / 2 and x = (5 - sqrt 31) / 2

Hope this helps!

[Deathless2288]

it should be x = (-b +/- sqrt (b^2 - 4ac)) / 2a

[NeoXC]

Oops! Thanks for the correction! I had a bit of a brain fart there

[NeoXC]

Hello, great video, Khan! I have a few problems I'd like to ask... I'm great at factoring quadratics with x^2 and x terms, as well as substituting x with y to make the quadratic into x^2+Ax+B form, but as soon as I hit precalc, I'm being faced with difficult problems I don't know how to solve (the book doesn't explain much, either).

Factoring with fractional exponents:

6x(1-x^2)^(-1/2) - 3x^2(1-x^2)^(-3/2)

And factoring problems that look at simple as this:

1-x^6

Thanks!

[airfreak789854521]

excellent job man! 100X better than my lame teacher and the textbook put together! xD

[MrCpaw]

Thanks for providing a great video! A lot better than my text book, they don't even explain about how to get the (x + ) (x + ) = 0.

[quartoGBbrooklyn]

if i found these earlier my algebra regent would be perfect, but i just found these through someone i know and i have the regent in 2 hours =X

[flamingshadow4068]

u should b my math teacher instead of reading from a text book

[YdLeet]

Thanks ever so much Salman! :)

[diamondbell5]

This is great, thanks so much!

[flamingshadow4068]

something like this was on the star test now i get how to do it in stead of taking an "educated" guess lolz

[lisinka3]

At your website, in the solving a quadratic by factoring module it spit out a problem of the type.

f(x)=-9x2+441

I can't find how you would solve this in the video, and it doesn't give a hint.

Can somebody help me out?

(Answer is supposed to be x=7,7)

[lisinka3]

EDIT: It's supposed to be f(x) = -9^2 + 441

[sterm01]

If you factor out a -9 you get X^2-49, at this point you just factor normally, (x+7)(x-7) because (a+b)*(a-b)= a^2-b^2 so basically the posotive seven and negative seven will cancel out thats why you only get two terms.

[dmiv424]

wow this is so much easier than trying to read a math text book.

Something about mathematicians ego's prevents them from writing a layman friendly math book. (at least the books used at my school)

Good job

[youstink14]

"Something about mathematicians ego's prevents them from writing a layman friendly math book."

got that right for sure

i was just checking out some these khan academy videos and they are great and easy to understand

i could've have had an A+ if i had found these earlier

[vickiormindyb]

@dmiv424 Medical doctors egos must be the same, b/c they can't write the textbook for paramedic training much better.

That's why I keep hoping Sal will do the math related to IV Therapy, which was nothing less than hellacious to learn in Paramedic School.

[backlikevertabrae]

@dmiv424 So true, they always complicate things so much.

[blackdranfire]

Do one where the equation is not set to zero like

x^2 + 5x = 6

so they have to zero out the equation

first before they solve.

[nejtilsvampe]

blackdranfire you can just say x^2 + 5x - 6 = 0 and then solve it like normal.

[blackdranfire]

I know I was telling them to make an example like that so kids now what to do when they face a question like that on an exam.

[NJmalibu313]

Thank you both black and nej for pointing this out

[AsEOfSp8dES14]

bluemicrowave is right, the parabola is on the wring side of the y-axis but that wasnt bad for an estimate

[angle4everr]

Can u plaese put up videos on factoring polynomails and ditstrubtive property.

[BlueMicrowave]

are these called zeros? also, i think the x's were placed on the wrong side of the graph.

[EasytoonGuy]

I apologize my use of language if it offends anyone, but holy fuck, I finally understand this. Thanks a lot, Sal!

[Teleranger4]

Nice one. Keep up with the good work !

[CtrlCreate]

Thaaaaaaaank you so much for this!!! I was having trouble factoring trinomials of the form ax^2 + bx + c where a doesn't equal 1. It's so simple! Just divide all terms by a and factor, then multiply a by one of your factors :D

[vickiormindyb]

I don't remember this at all. I vaguely recall a formula of FOIL; which meant first, outer, inner, last.

Is that what this is?

[carapink2010]

Basically, it's undoing the FOIL method. I remember how to factor the equation when a equals 1 but if a is equal to anything other than 1 I can't solve it!

[CtrlCreate]

I know this is a month after your comment but I think I can help you when "a" doesn't equal 1. It's not the best way to do it but it always works. When a > 1, divide all terms by a so you remove it. Factor the new equation then put "a" before one of the factors. The finished product should be "a(factor1)(factor2)".

[carapink2010]

Thanks alot !

I going to try that

now and see how it

works out for me.

cARA

[suckmyloli]

As far as I know the FOIL method refers to when the question is in the form of eg.

(x-2)(x+4) and you need to get it to an equation you can solve using the methds in the vid. So in this case you would get x^2+4x-2x-8 then you tidy it up x^2+2x-8=0 and from here you can factorise to find the roots.

[idricool]

Thank you !