Added: 4 years ago
From: khanacademy
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  • Helpful video, thanks. This helped me with figuring out the calculation of slope for aircraft descent rates. Pretty cool how this stuff works sometimes!

  • @MileHigh537 Sure is i love mathamatics :)))))

  • i wondered who is this genious human's wife...hint?

  • Why did I not have this lesson at school? answer: Cirriculums Useless N Teacher Sucks. What a waste of money school was!

    Let's hope the great Sal Kahn or can model gets into more schools!

    and the CUNT model fucks right the hell off!

    with the shit teachers!

  • Another way to state it once you get round the mathy stuff! is that there are 2 x pi or 6.28.. radius lengths in one circle and one radius length around the circumfrence is 360 degrees divided by (6.28).....( or 2 x pi) = 57.2958 degrees per circumfrential radius length which is a radian!

    if your in to cars and engines ect the radian is used to determine the number of metres per unit force a turn (torque) and multiplied by the number of turns / time to give watts or horse power!

  • Wow, thanks so much, it makes much more sense to me now! :)

  • Stupid question but what does sub-tan mean?

  • @Swh3913 No Wait never mind heard him wrong

  • Hi there Sal great video as usual, I don't know if you were just pretending not to remember how to convert to radians for the sake of the video ;) but just in case the way I remember it is that radians usually look like A pi/ B so to convert to radians you multiply by pi (on top) then divide by 180. To get degrees its just the opposite of that.

    BTW the plural of radius is indeed 'radii'.

  • i saw a REALLY neat trick while he was doing this when he was giveing out the problems like 45 or 2 or 30 your answer for the problem is how many times it goes in to the number of degrees the circle in questions is!

  • Lol. Radius's

  • @musicmelodyx  Radius'

  • More thank THANK YOU MRS.

  • Light bulbs just went on. Things make way more sense once I understood what a radian was... Wow but that makes it a lot easier to understand!

  • YOU ARE HILARIOUS !!! XD

  • my wife came home so i have to stop teaching u via video that i can edit? really...

  • THIS IS GOLD. I GET IT NOW. THANK YOU :D

  • Thank you do so much, you explain everything so well and you have such a pleasant voice :)

  • its radii btw.

  • He managed to teach me in less than 10 minutes what my Geometry teacher couldn't in one hour...

  • what program do you use for this?

  • Iunno, when I use the exact value 57.29577951 on my calculator, it gives a dead-on accurate result everytime.

    Apparently this value, is somewhat an ideal standard for degrees that don't exceed 10,080,000 degrees, and radian values that don't exceed 175930 (estimate).

    It's surprisingly accurate.

  • Could you please redo this I am not getting it at all.

  • @Unit047 don't call your girlfriend or wife a bitch. that's not very respectful and makes you look like a douchebag instead of a cool guy. If she got home, im guessing she makes the money and you sit at home like a fatass

  • @btrballin

    Dude! He's just restating what Kahn said in douchespeak. LOL

  • @Thornshadow17432

    o_O

    Or is he serious...o_O

  • @btrballin How much do you think she charges per night?

  • @btrballin why mention it in the video at all?

  • do geometry first kiddies. ha ha

  • Teach the kiddies about steradians later on.

  • i still don't get it....

  • awwww. you have a very lucky wife.

  • THANKS SO MUCH!

  • This is great! no more going to sleep confused and pissed off! :D

  • I can't listen to this one sorry sounds like you are eating something.

  • can you upload this in 720p? Thanks Sal.

  • LOL, he needs to go attend to his wife. <333 what a good man.

  • @WHHB1223

    lmao that was funny.

  • i can finally have help

  • Well he just has the gift explaining math in minutes, but has he discovered anything new? no offense Salman Sorry.

  • @spyrolatro oh yes he did,u will be dead oneday lol lol

  • "subties an arc of two pie radiasisis or radyi" - haha... to funny.

  • Pacman. FTW.

  • its radii my friend

  • @darkness902 Radians and Radii are two different things. In a circle with radius r and center at the origin, a Radian is the measure of an angle in standard position whose terminal side intercepts an arc length of r. A Radius is the distance from the center of the circle to a point on the circle. So the plural form of radian is radians and the plural form of radius is radii. Hope this cleared things up!

  • @darkness902 WHOOPS I thought you meant radians should've been radii, but I realized you were referring to something else! Sorry!

  • ....your circles were better before XD

  • When I finally understood the concept of 1 radian on a unit circle, I said to myself "whoa, this is just too good for words!"

  • wait.. isn't pi is 360 degree?

    i mean pi = full circumference = 360 degree.

    why 2pi rad = 360?

  • @MidnightRedemption Because Pi is, in a way, flawed. If you used Tau, which is equalivilant to 2Pi, it would make a LOT of Trig a LOT easier. But not many people know about Tau, and therefore Pi has stayed. Look it up, Pi vs Tau, it's really quite interesting.

  • Comment removed

  • Is it wierd that im a sophomore in highschool that is learning this?

  • @HappyTissues Same here, not weird.

  • @HappyTissues I'm learning this for fun in seventh grade.

  • @tigerstar216 You sir, will go far in life if your desire to learn new things is so great you enjoy learning about math. No sarcasm intended, I just don't have that same drive. Good Luck.

  • @HappyTissues Thank you very much. Math is actually my favorite subject. I hope to have a math-oriented career. Kepp trying in math and eventually you will get it.

  • @tigerstar216 I wish this stuff was available in 7th grade. Now I'm watching Khan for university!

  • are you married to Mrs. Fenker?

  • you have got to be like the best math teacher in the world. All your videos could just be watched once to be able to get what you are explaining. But i find myself watching it more than once so i could it understand it as good as you. I dnt think nyone watching your videos could thank you enough. Also im wondering why teachers in general dnt explain it as well as you do. Thanks.

  • thanku very muchhhhhhhhhhhhhhhhhhhhhhhhhhh­hhhhhhh 

  • emm my log table say that 90* is pi over 2?????

  • @coolwHip200 because 180* = pi rad, so if you divide both sides by 2, 90* = pi/2 rad

  • Sal take care of your wife first!..she is going to scold you!

  • How do you spell the word at 1:24 ? Sub -

  • "Let me just finish this problem, then I can go attend to my wife"

    *a minute and a half later*

    "Let me just do one more"

  • This video just singlehandedly helped me with my homework.

  • You're better at teaching than my current math teacher. thank you.

  • in the begining you explained the definition of subtense with the word subtense... made me rewind twice lol

  • That would be radii! :)

  • great tutorial, question: can I use inverse sign to convert rads into degrees?

  • This helps but not enough! Explain complementary and supplementary!

  • Khaaan!, are you on the computer again? Sometimes I fell like you just don't care about me!

  • Awesome job! After two periods of math I still couldn't understand it, yet you explain it way better than my teacher in ten minutes =)

  • THANKYOU my teacher never explained this

  • Its like a teacher that I can rewind... Its soo awesome

  • Finally, i finally complete this milestone once for all. Thanks for explaining it. I spend hours in tutoring none of them ever said any of this.

  • Hahaha your such a silly man! :)

  • radiuseses!! Haha awesome video.

  • very nice 

  • u are the best.

    ....the best, the best, the best

  • @CryptDoidge

    You confuse me. What are you saying? All of this that he just said is completely correct. Sal is a genius, and is not teaching in a classroom because

    A) This is an alternative

    B) He reaches more people this way

    C) He has no formal teaching degree (yet ironically teaches better than most teachers I had).

    Lrn to Lrn. And type.

  • @CryptDoidge manners...

  • @CryptDoidge troll alert

  • Comment removed

  • @CryptDoidge wow don't hate because nobody asks you for help or you don't get any attention. -_-" This is an alternative way for kids to get help for school.

  • hmm

    Owner of Khan Acadmey is Muslim and He is serving Humanity Good job bro

    Keep it up

  • @Jawwad16

    Muslim? Where'd you get that from?

  • @hedonism13 his name is khan DUH

  • I wish youtube could be there years ago when we had our learning years. You are doing a noble job and you are truelly gifted and made for this respected profession. How do you generate a revenue for yourself?

    God Bless.

  • @TheLoveispure His website is completely nonprofit, but he takes a salary.

  • lol.. "oh, er my wife just got home, so i'm just gonna have to leave the presentation like that, and i will continue it er, later, i think you might get the point - actually let me just finish this problem, and then i'll go attend to my wife" lol.. the perfect nerd, i love it, sal, you're gonna get me through my senior years!

  • Lol Nice... Haha WIfe getting home... YOu dont seem old though.. are you like what 20?

  • Sal, you are the man!!

  • Yeah khan, you just have this enchanting voice that makes math easy. No joke. :)

  • This really is helpful. When u explain it, it all seems simple + ur voice makes it sounds simple for some reason, but when my teacher speaks her voice is just soo annoying that i cant even focus. GJ, keep em comming.

  • Why not in the last problem, instead of multiplying (pi/2)(180/pi), just substitute pi by 180. I tested this "theorem" and if you have , for example 13pi/5 = ?, just multiply 13 (180) and then divide by 5: 180(13) = 2340 divided by 5 = 468 therefore (13pi/5) = 468 deg . now we check: 468pi/180 (/4) = 117pi/45 (/9) = 13pi/5. What do you think?

  • @jaidrofire "Why not in the last problem, instead of multiplying (pi/2)(180/pi), just substitute pi by 180. " You can substitute "pi rad" by "180 deg", since we said that pi rad=180 deg. That's great and I think the teacher won't say that you are wrong if you do that, but the problem comes when there is NO pi in the equation. For example, you are asked to change 2 rad into degrees, and your "trick" won't work. Other than that situation, your "trick" is fine.

  • @dalcde In that case to change from 2 rad into deg is another formula (yeah that trick won work here). x rad = x (180/pi). in this case: 2 rad = 2 (180/pi) = 114.6 (estimated)

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  • I finally get this!!! Now excuse me I'll be watching the rest of ur vids on trig^^

  • i prefer watch all of your videos than read my books...

  • @aceyabank SAME HERE!!!

  • That bit about the wife getting home was hilarious!! LOL

  • Thanks man this video helped me out a ton!

  • lol you chose math over your wife

  • Dude, this video really helps me, I got really comfused with this stuff. Rock on man.

  • hehe its "ray-dye" i think...

  • i be lovin' yo 1337 ghetto drawing skillz ma man. Peace and love to yo and yo wife~

  • OMWife jus came how so lemme jus finish dis and urm...TEND to my wife LMAO =D

  • omg my maths teacher tried to explain this to me but i didnt get it at all and was really worried as everyone else seemed to get it but now i think i no what i have to do thankyou x :)

  • man i was in the hospital for 1 whole week so i missed school. Now, im falling behind in my precalculus class, after watching this video, i feel like i alrdy catch up with the class! thank you Mr. Khan! thank you!

  • this guys narration is funny lolz

    this was a big help

  • It makes so much more sense to me now! Thank you for making these awesome videos!

  • OMG, I love you! That helped so much! = )

  • Thank you Sir, U sure do deserve the math Nobel Price.

  • You sir, are a genius and deserve a Nobel Peace Prize haha.

  • @sambam22031

    i second this lolz

  • bahahaha my math teachers so dumb :)

  • Thank You! Thank You!Thank You!Thank You!Thank You!Thank You!Thank You!Thank You!Thank You!Thank You!Thank You!Thank You!

  • thank you so much.

  • This made me learn Trig so quickly, you're so awesome. (y) I need to cram a year's worth of Math in my head in less than 10 days to pass the AP Math exam.. Wish me luck. T_T

  • We know who wears the trousers here  lol Thanks for the help

  • Its officially 6 in AM and i am learning trigonometry and i love it, thanks for teaching.

  • MY favorite part was when you said "then i will go attend to my wife"! that is the cutest thing ever. 3 thumbs up! thanks for the trig help too.

  • Radians are used because it is both a unit of angle and of distance. This matters when you start to graph because you use it for both the angles and the X & Y coordinates on a graph.

  • Great video! You should do one on graphing these bad boys as well. :]

  • I've been trying to dust off my old calculus skills and discovered that my trig skills were all corroded, too. I want to thank you so much for the lesson!

    I can't wait to watch your other videos!

    Keep smilin',

    annie

  • This helped me, thank you.

  • math > women. FTW

  • @pokaymahn Can't get laid

  • THANKS ALOT yo this helped

  • Im starting to believe u are my hero! im takin chem 1 and trig this semester in college, and am having a hard time.. and you are saving me in both subjects. i love ur humbleness in teaching- you accually act like a human, not a stuck up know it all teacher! thanks khan,, ur da best of da rest!

  • It's amazing how you can be a math expert and still forgets the formulas except the basic ones. You gave me hope because I am also like that I usually remember the basic formula and forget rest and have to rewrite the basic formula everytime to reach other formulas. So I always thought to be math expert you need to remember everything but you proved otherwise. Thanks a lot. I love watching your videos.

  • I was having some difficulty gaining intuition to the relationship between radians and degrees. I came up with this formula to help me remember.

    X(1 degree) = (pi / 180 radians) x (equals multiplied by equals give equals)

    X degrees = (x pi / 180) radians so

    45 degrees = 45 pi / 180 radians so 45 degrees = 1 pi / 4 radians.

    Thanks again Sal! Peace.

  • so 1 radian is 57.295 degrees?

  • that last example is incorrect:

    30 Degrees is 150 times less than 180 deg so 150 times less than 1 = 1/150

    so 30deg = 1/150

  • I ment 180/30 = x

    And 1/x = 0,375

  • 30° * 150 = 12 full pizzas and a half mate.

    30° * 6 = 180° so the last example is correct.

    Enjoy your magically multiplied pizzas.

  • this is amazing.. great tutorials you've helped me a lot thank you =] everything makes sense now man!

  • Ha! You said "Oh my wife is home," like you were gonna get busted for teaching trig. That's funny.

    Great videos

  • @jmk1a1 lol "Sal are you teaching trigonometry again >:(" haha

  • @LuisRC91 "Oh, Honey it's not what it looks like. Trig and I are just friends. We met on the Internet!"

  • you don't need to make any changes but you should have the wife watch this particular video, I'm sure she would think it's cute how you almost went into a panic in your eforts to "tend" to her!!as usual, your videos are clearly superior to any others of their kind!!

  • I love all your movies, ive watched most of them, thankyou, they have helped allot

  • You saved my life !

  • i prolly should have went to class this week... bad time to skip every lesson on trig and try and pick it all up in less than 5 hours... so far im kickin trigs ass because of your vids

  • Your wife just came back!!!!! Seriously dude, you should inform her that she has just interrupted a very informative and valuable moment of my life. Thanks anyway.

  • best tutorials on the web

  • great shit helped me pass my test in trigonometry :))

  • thanks man. i really need to know this for my math exam

  • This video saved my life!

  • lol you guys! just chill man... y so agro dawg... just watch learn and pass mathematics niggas!

  • well said ahha

  • John 3 :29 GO FUCK YOURSELF

    I made that one up myself (thank you very much)

  • thanks alot man. i have finals tomorrow and our teacher told us he need to perfect radians and degrees and i just did

  • you are a fuckin godddddd (A)

  • Shutup you stupid christian bastard

    Dont think you own the word god

    Anyone in the world is aloud to praise what they want

    And the last think we need is a sceptisict who is trying to start a superoirity contest :|

  • dude, the guy didn't even capitalize god. I mean, all he had to do was add an "a" and he would've been fine. Who knows, it might've even been a typo.

    Not flaming ya, it's just that this is a very skilled interesting teacher, let's keep it down and learn.

  • Buns

  • thanks this will help me ALOT

  • oh, well then I am smarter than I gave myself credit for. I can always find the long decimal answer for any radian. I just thought every answer had to be given in terms of a pi equation and it just seemed like that would be really a big pain in the butt for random angles. I went from learning the degrees/minutes/seconds back to radians where I was barely able to express 45deg. lol I guess I just overreacted out of frustration. Thanks!

  • So... every example I find is always with the simple angles like 90, 45, 30 etc... what happens for like 33 deg or some odd random angle that requires pi's denominator to be a decimal??? Maybe I'm just dense, but I am having a lot of trouble figuring this whole radian measure thing out. I can calculate answers to the more odd angles, but then I will get a long decimal sometimes and I get all confused. Any advice?