Introduction to the quadratic equation

[angeldog1]

THANK YOU SO MUCH. I LOVE YOU.

[biolexyable]

thanks so much you really helping me prepare for my next sat which i know i'm not getting anything less than a 650 in the maths section

[MilleniumDream]

i love how math teachers make this so much more complex than it really is xD

[candiceroe]

I am so lost....... lol I got this in high School and 5 years later its alien jiberish to me

[1997littlea]

@candiceroe lol, i am learning this in middle school ;D

[ahmadu007]

man you speak damn fast. but that doesn't hinder the extremely legendary tutorial!

[alpenroseboys]

THANK YOU SO MUCH this will really help for my high school placement exam tomorrow!

[Death7Sage9Mode]

i'm in year 9 why is the a square root???

[frantzzzze]

Thank you, thank you, thank you!!! Do you have a video showing how to find the coordinates of the vertex???

[tr3ndkilla]

At exactly 3:00 I went ooooooooooooo. 3 minutes of khanacademy = 2 hours of school math class.

[iWriteUinMyDeathNote]

woot finally get it... it works when you watch and master previous videos

[thejonathan130]

if I would of heard "I KNOW IT'S NEGATIVE 6 BECAUSE X = 0" I would not of faild my previous freaking test!!!!!!

[thejonathan130]

in case he gets shut down by some damn teachers union DOWNLOAD HIS VIDEO'S!!!!!! (damn keyboard)

[thejonathan130]

in case he gets shut down by some damn teachers union DOWNLOAD HI VIDEO'S!!!!!!

[Catatonyx]

Screw the textbooks. This is infinitely better. And I actually enjoy listening to them. Hello, A+!

[chills2102]

your videos should replace my instructor, good sir.

[sunshineeeast]

Please put how to factor polnomials using a graph without calculators, just a plain graph and its curves and intercepts :)

[Silents30]

Why do I pay so much for college when I learn more from Sal for free.

[Silents30]

2 hours of class, I don't get it. 3 minutes of video, I got it!

[SuperCommentwhore]

/watch?v=N30tN9158Kc&feature=r­elmfu people who are confused about the factoring in the start watch this.`!

[haloiscoolerthencod]

SALMAN KHAN IS WINNING!!!!!!!!!

[SmithGarridoLe96]

Nice

[nshikanai]

pfft, become a teacher. Just show them your youtube videos. Easy job. Lol

[XplicitGlam]

THANK YOU

[FirebirdX]

Nice video! I would love a cubic equation video like this one too.

[45appaloosa]

thank u now I may have a chance for geometry instead of having to repeat algebra

[88joeana]

YOUR SO LEGIT! xD (;

[xxMiZa]

What was those first equations you were doing called ? Like the very first equations.

[JaneApter]

I was a middle school / high school math teacher for 19 years, so I'm well-versed in these mathmatical formulas that are essential for students to understand & use successfully. Yes, it was kind of messy. :) But your demonstration was simple & nicely demonstrated. Great job!! I will be recommending you to several family members & friends who homeschool. Thanks for enriching their learning!!!

[absolutemes]

@Neptutron because you need to make x in x+2=0 isolating so you need to subtract 2 from both side and you will get x=-2

[88joeana]

thxx :)

[beetzart77]

Mr Khan you are a genuis and a savior...thank you!

[bolmung]

I agree with George W. Bush :o

Teachers need to go to college longer, and end up like this guy.

[titaniumnips]

love this man

[AniodD]

hehe, he said =3

[raysbaseball29]

theres a song!!! sing it to pop goes the weasel!!! makes it easy to memorize

[ShakkIsLife]

Khan, you forgot to add the +1 onto 121 :P

[reposteve]

Good job!!! You're great I understood and followed your example I made good notes from your presentation. Thank you, keep up the great examples.

[hbaloro77]

i don't get why the x value would flip signs? for example the x= 2.

when you factored it was (x+2)(x+2) then you made it -2? i dont get it :(

[ShakkIsLife]

@hbaloro77

It doesn't.

[trevdog110]

@hbaloro77 because hes isolating x. since it was x+2, he had to subtract 2. pretty simple stuff

[10bennyb]

what are you talking about ??

Im lost

[soccerfean]

U SUCK MAN DIDNT LEARN NOTHING YOU HAVE TO ELA BERATE MORE !

[raydredX]

@soccerfean Stop playing soccer. Then you'll understand.

[donttellmethetime]

What does the -6 represent on the graph? He says when x is = to 0 but i dont understand that

[zamrock20]

@donttellmethetime x=0 is the y axis

[juliabuffam]

You are a god. THIS HELPS SO MUCH!! THANK YOU!!

[ALEXCHASE750]

FUCKING SAVIOR!

[lacrosse123brine]

@ALEXCHASE750 AMEN

[MrZia324]

u are a real KHAN. Keep it up brother.

[gundamnoober5]

@chrismerk420: it is a function, silly. You literally are looking for f of x eg: f(2)

equation: f(d)= 2d+1

replace d with 2

f(2)=2(2)+1

2f=4+1= 2f=5

divide each by side by 2 for f

f=5 over 2

plug it in= 5over 2 x 2= 10 over 2 or 5 and on the other side is 5, so the formula is correct

5=4+1, or 5=5, combine like terms.

[OuttaEgypt]

Sal, you're AWE-SOME.  First video and I already understand what's going on. THANKS!

[chrismerk420]

what is "f of x"?

[croydonkidd1]

thanks for the help

[AbbASongs1]

If you want to remember the formula I advise you to type in the search engine, Quadratic Formula song, and believe me its worth viewing, they really help to remember ;) Oh Thnx for the intro for this, because I really suck at maths.. and i desperately want to do well for once in my test.

[2nahj]

nice



[devito108]

i love you khan. u are like the greatest tutor ever. way way better than the sh**y pay as you go teachers out there.

[SpoiledLogic]

Great video Khan! But for that quadratic function (-10x^2 - 9x +1 = 0), it is much easier to use the box method rather than the quadratic formula.

[starstruckdiva101]

Thank you so much for posting these math videos! I can not even begin to express how much your videos help me study for my math classes.^_^

[techking00107]

I have two options study and learn from youtube or copy from my friend who sits next to me in class. I really want to learn but I am not good at math

[TheFlameEffect]

Awesome work... I hope your website works well..... I guess you should remake some of your videos and put your website on subscription based......

[TheFlameEffect]

Thanks man....

[mixolidianmode]

what is the meaning of the f(x)?

[mixolidianmode]

i wanna get really good at math

[AbbASongs1]

@mixolidianmode you and me both, I suck at it, everytime i see a formula or equation I want to burn the book

[Drewes01]

Nice video...

I found a very interesting app for Iphone that allows you to solve quadratic equation in a very simple way. check it out...the name of this application is Equation (by objectouch)

[B0nafideJones]

what video comes before this?

[NataliaThe777]

thank you so much!

[setimeti]

0-4:33 was bad.... 4:33 till end really good..

[hotred202]

I'm in 8th grade and your video is what I needed to understand!!! So thanks!

[Seniorbooboojuice]

you are too hard in yourself man that didnt confuse me this is the best explanation i've ever seen. thank you for these videos.

[garythegengar]

Thanks!

[DeViLiN888]

Sal could you make some videos on 3rd degree polynomials and how to solve them?

[Maaaacs]

That's wrong, sorry, 2:50 : The minimum isn't -6 but -6,25.

[Goal2Tend]

@ Maaaacs

We know it can't be the minimum, but if we place 0 as the x value we can get the y value at that particular location. The graph he drew wasn't quite to scale it should have been slightly to the right. and -6 was not the minimum.

[furyofnasa]

On your second equation, where you got (X+2) (x+2), x = -2. But it is a quadratic graph, why does it only intersect at only -2 of the X axis? Shouldn't it be 2 values?

[furyofnasa]

@furyofnasa NVM lol I got it

[Ivan436]

i really don't understand why the vids on functions are only *after* this one.

[keepup20]

you do not know how helpful you are never stop making these video

[BlueTunisia]

OMG THANK YOU SAL!!! Now I don't have to fail anymore math tests!!!!

[blklist08]

ahhhh sorry I figure it out, your correct its -20

[blklist08]

7:11  -10 x 2 = -20? I think its positive 20, negative times negative the answer will be positive right?. please correct me If I am wrong

[SoftShredding]

-10 x 2 = +20? :S

It's a negative multiplied by a positive, which will always be a negative; hence -20. The guy got it right, good video.

[blklist08]

I know...iIi..., thx for reminding me

[auduuun]

I wish that I become as good a teacher as you are!

[how2ninja4dummies]

Yes.

-9^2 = 81.

Remember that a negative times a negative is a postitive.

[alique087]

-9^2 is not 81.

[sherzodibrohim]

multiply (-9)(-9)=81

[paulfbcynthiamt]

Im not even in high school and I still get it. Ur a great teacher.

[angelum6]

My brother asked me to learn him about Quadratic equation for school. Since I haven't solved one since high school (7 years ago), your introduction came in real handy! :D Thanks!

[MyNYCE]

Thanks for all your help khanacademy!!

I am struggling in math at my college.. i'm in remedial math so I'm working my way UP! it's pretty frustrating because a lot of ppl are taking calculus and stuff while I'm stuck in intermediate algebra.. but anyways, your videos help me and you are a very good teacher!! Thank-you so much!!

[MrErnie1994]

I am afraid to say that I see a minor mistake in the polynomial x-squared minus x minus 6. The error lies in the graphing. The parabola's vertex is (1/2, -25/4) not on the y-intercept as you pointed out. The y-intercept is merely where the parabola hits not where the parabola starts. You can find the vertex by using the formula -b/2a.

[asdff1818]

I wish you were my teacher, you are so good!!!!

[anothercalmstep]

I've always wondered if there was such a significant thing to justify getting a tattoo; I'd say that equation qualifies :P

[mis3catz]

0owh..

n0w i really2 understand it better!!

TQSM!!

u r a great techer^^..

[Winsunn307]

Very helpful, your a great teacher, thanks.

[SpareTimeFilm]

your a great teacher

but hate how all teachers use the big words

i get so confused

i wish instead of variable they said the letter

or instead of coefficient they said the number

[merkercana]

i agree very much, but it was a great video, and very interesting

[syredeathtrooper]

thats maths terminology..

i think its unfair if your blaming teachers for using them and not the students for not learning them

[idricool]

You're great I hope you get to be a professor because you tech better than some.

[idricool]

You're great I hope you get to be a professor because you tech better than some.

[marsunderscorefenix]

@idricool teach* most* / all* I hope you become a professor* - Your english teacher has done a very good job.

[zerolizard]

Great job! Best math series on Youtube.

[desoan]

thanks a lot man. this helped a lot