Using Trig Functions

[peterana00]

lol guy teach better than my math teacher

[Wulfex]

SOH CAH TOA

Some Old Hippie

Caught Another Hippie

Trippin On Acid

That's how I remember it :)

[killarunao]

@Wulfex I just remember it as fucking SOHCAHTOA dude

[Wulfex]

@killarunao ... you must be an old hippie...

[DarklightALBANIA]

Bless your face

............(How many will get this reference)

[AllHeilKitler]

@DarklightALBANIA reference to toby?

[thisbobful]

this is my version on how to do tangent questions

watch?v=S5GEnJdyGcg

[iamtrxjnbaldz]

Thank You so much!

[SwirlingChords]

OMG That sneeze scared the shit out of me!

[HardstyleMenace]

1:33 i pood myself :P

[xxBlueHaze]

Is there such thing as cotangent?

[chris57283]

@xxBlueHaze Yes, cotangent is cosineΘ over sineΘ instead.

[shapeurmind]

in my country we have to memorize sin, cos and tan of 30º, 45º and 60º.... :/

[JaySmith91]

@shapeurmind You just need to remember one lot, which follows a simple pattern i.e.

Sin (0deg)=sqrt(0)/2 = 0, (30deg)=sqrt(1)/2 = 1/2, (45deg)=sqrt(2)/2, (60deg)=sqrt(3)/2, (90deg)=sqrt(4)/2 = 1.

Cos: Reverse the order

Tan: Divide sinx by cosx to get: 0, sqrt(3)/3, 1, sqet(3), undefined.

[winstonmetalcore1]

@shapeurmind same here :( and we cant even carry scientific calculators :( so pissin offf math is :(

[IndiexhannahxJones]

omg bruhhhhh!!!!! i bout died at that sneeze guhh the scarry thing is is that i read RazorbackV13's comment a second before he sneezed omg. heart still pounding. lol

[alvonyuszi]

cos (pi/4) isnt something that people memorize??

in my country we have to and we cant even use calculators on lessons. we have to remember sin 30, 45, 60, 90 degrees and same for cos.

im sorry but its really weird for me because i'd get a bad note if i didnt know it!

[eruptoin]

@alvonyuszi glad i don't live in hungary coz that sounds hard!

[Esoparagon]

Blew my ear drum but it was worth it lol Good videos.

[awaqar]

@Esoparagon What does this one do with your ear drum? "Speed maths- Multiplying without multiplying". Click on my username and check the vid. Cheers.

[kushner266]

tan(.54) is not 3/5......

[jacob3800]

@kushner266 Google says it's 0.599429623, which is 3/5 when rounded off to 0.6.

[nessdude14]

@kushner266 Since the angle is only given with two significant figures, you can consider tan(.54) to be .60 rather than the more accurate .5994. Essentially, by using 4 significant figures in your answer, you're pronouncing accuracy that isn't actually there. It's a bit like declaring that 0.4 centimeters added to 0.2 centimeters is equal to 0.5994 centimeters.

[DJ044]

hey when you said "that kind of reminds me of", what where you gonna say dora? cuase thats what i was reminded of or one of those kids cartoons that ask you something than gives u the answer

[DJ044]

hey when you said kind of reminds me off, what where you gonna say dora? cuase thats what i was reminded of

[whathisfaces]

wow this is now hard going back to my own grade in 10th grade!! geometry here i go! (its ez)

[Fuzzietomato1]

I wish he was just using normal numbers insted of pi and square roots

[onthecuttingedge2005]

please, that allergies fit popped my ears.

[hotwanghour]

AWESOME AND BLESS YOU

[jbspine]

This video is of less quality than I have come to expect from you. The cough almost blew out my eardrums. Redo it.

[SuperHexadecimal]

cos 45=1/(sqrt 2)

[satisfiction]

THANK YOU SO MUCH FOR ALL YOU DO!!!!!!!!

[Parkwoodparkenfarker]

how can 180/pie = 90 I thought pie was 3.14?

[samuelzhang332004]

@Parkwoodparkenfarker Er... first of all its Pi. and where in the question do you see 180/pi? o-o..

[MrJivePirate]

Good work Solomon

[tjohn1986]

The answer to first question is 5 actually.

[lordbyronXIV]

A good way to figure out the sin, cos, or tan of angles like 30°, 45°, 60° (pi/5, pi/4, and pi/3 Rad respectively ) is to know the special triangles. (30/60/90° triangles, and 45/45/90° triangles. 30/60/90° triangles have sides x, x(3^1/2), and 2x for whatever x. The size of the angle of a triangle directly corresponds to the side of the triangle opposite to it. So the sin of 30° or pi/5 Rad will always be x/2x which equals 1/2 or .5. Same for 45/45/90° triangle with sides x,x, x(2^1/2).

[es696]

Having trouble with the last question... I have my calculator in radian mode and I enter Tan(.54) and get .5994296232. When i press Math,Frac, I don't get 3/5 like you do. How did you get 3/5??

[es696]

@es696 - ohh oh he rounded it... thanks for NOT making that clear in the video lol. made me think my calculator was broken for like 15 minutes

[AraiI3ian]

soh cah toa also is(start of every word): Some Old Hags Cant Actually Hide There Old Age

[ksargeant7]

the answer to the problem at 5:45 isnt actually 10 its 9.999999999... lol :)

[hetamalo]

What if your answer wasn't one you could put into a fraction like 5.994?

[Misana]

the last video I watched, he coughed. and I jumped! hehehe

[kashmutt]

why are we finding cos pi/2 when we want to find cos pi/2rad

[sharmaishan38]

You don't have a drawing......hahahhalol

[DeptBookDave]

@PowerOfTheChestnut

Thank you. I found the answer to my question shortly after posting my question, but I'm willing to bet that other people who didn't understand will be helped by your reply. Again, thank you.

[futast]

im going to watch every single video you have man so helpful

[karama33]

you roound tan(.54) into 3/5 and confused me at first but i cuaght on to u

[PureTamil]

9 people disliked the sneeze lol

[paulceltics]

Watch OUT! 1:30

[Mus3ab25]

idk .... when i check this on my calculator , i come up with a different answer !!!

i mean ... 10''squareroot''2 x cos ( "pie / 4 " ) = 14.1 aCcordin' to my calculator !!

[georgew0304]

I love you man :') If I get this in my paper tomorrow, you will be totally awesome. Thanks :)

[Emzypempzy]

i wonder how old sal is and what he looks like!!!! put up a video of urself man :D ur videos are amazing!

[hammd123]

@Emzypempzy click on his channel you will get all his videos. His name is Salman Khan, in short Sal.

[Emzypempzy]

@hammd123 thankin u :).. i just ment what he looked like!,,, hes sum dude :D

[lilsadiq]

im wearing some air yeezy's and and all red pro beats head phones.......but this is priceless

[DeptBookDave]

Small question.

At 3:43, what exactly is meant by the cosine of 3.14/4? I was under the impression that trigonomic functions such as the sine were applied to angles.

Sorry if I seem uninformed. I've never studied trig before and I'm just trying to get a foothold before I do.

[PowerOfTheChestnut]

@DeptBookDave The 3.14/4 is expressed using radians, not degrees. They're just simply another way of measuring angles.

[SourNaik]

Best Channel on YouTube for passing chinese professor math!!!!

[TheLamazoo]

Gazuntite

[MsJohn444]

mini heart attack @1:34 :P

[Caboose129]

im going to fail my test even though its multiple choice this is soo confusing

[babyjebus2]

I made a 94 on my trig test but i had to study hours i wish i had found this video first thank you for the review

[ForEvaW15h1nG]

am i the only one that wiped the screen after his sneeze

[Cloud9er]

how come 3/5 = tan(0.54) but tan(0.54)= 0.009425057 but 3/5 = 0.6?

My calc is set on degrees btw...

[OnlyXfox]

@Cloud9er what calc do you have? when you do this backwards you have to use tan^-1 , if you use casio, press shift, then tan :)

[SentientRaven]

@Cloud9er: The numbers mismatch because you're on degrees, he's using radians. :) Set it to radians, then tan(0.54) = 0.59942 or approximately 0.6.

[Drewdawg123]

@makelt jungle your calculator is probably set to radian rather than degrees

[MakeItJungle]

Hmm.. for tan(.54) I got .5994 etc... not quite 3/5. Is there a reason?

[MammaLuigiRobotnik]

CAH, ok. The C is for what?

*C is for cookie.

[IggySeeker]

GOD BLESS YOU GOOD SIR!!

[IggySeeker]

GOD BLESS YOU GOOD SIR!!

[Athenagal22]

*Blinks* URGHHH. I find this confusing :(

BUT I somewhat get it, which is waay better than how I feel at school :S

[Nenjaw]

You sound like this friend I have from the Netherlands.

You're a goofy-kind of funny.

It's awesome. :)

/like

[KeshaIsHot808]

49 people have shitty math teachers

[cotarna]

To calculate the Pi/4 is first 3.14/4 ) .785*57.3(how many rads per °) and that becomes 44.9805 and then you round up, because you round down previously.

And that is how you got the angle. Right? I just want to see if I got the angle° correct. Only thing I have had a hard time getting is the correct °.

[AngelusLabyrinth]

ah! my school requires us to memorize the values of the special angles! Unfair!

[rosschambers1987]

Haha at the sneeze, I crapped myself!!

[jp70117]

Turn your speakers down when ol' boy sneeze

[adi24296]

1:37 :))

[RazorbackV13]

That sneeze scared the shit out of me

[jeanpsurf]

@RazorbackV13 Funny dude!

[ThomasTheTank142]

use rational numbers!!

[ipreferns]

brutal teaching

[jonimoto]

mjhhhuhuihh

[KoopaFreak]

for those confused cos pi/4 = 1/(sqrt2) because 45dgr is a special angle with an exact trigonometric value that ppl memorize. other special angles include 45.60,30,90,180. Even further the reason why he put (sqrt2/2) is because when you multiply 1/(sqrt2) by (sqrt2)/(sqrt2) -which is essentially one- you get (sqrt2)/2

[tysonaussieguitar]

saggy asses heal cunts asses heals trough out asses

[sajabz2007]

Where was you back in high school! :(

[AcutePorphyria]

@sajabz2007 *were

[belliveau5]

at 3:55, could you convert the pi over 4 into degrees and then calculate the cosine?

[bmx4637]

@belliveau5 pi over 4 is in radians. as long as the calculator is in radian mode than cosine must show radians only --> cosine(pi/4). Change the calculator to degree mode and you would have to put cosine of 45 degrees --> cosine(45) instead because pi over 4 in radians is 45 degrees. Just make sure these units are in correct mode

[belliveau5]

@bmx4637 Yeah it's what I figured! thanks homedawg. 

[CryptDoidge]

wow i bet this retard sends himself comments to make himself look good dont waist your time guys he is wrong

[15godfather1]

or you could just figure it out yourself (the cosinus i mean).

[NPowah]

@khanacademy According to my book "pi" over 4 equals 1 over squareroot 2. ??????

[121var]

nice video./....helpful for biology students....



[datHulkinZ]

wtf so bulshit in 1 plase p=180 p/4=180:4=45 a=b , a square+b square=1 square

or , a square+a square=1 square => a = square root of 1square / 2 which is square root of 2 /2 he don't know what he say,just read what he was saw in the books

[mrhnm]

@datHulkinZ you fail

[HANA3364]

@datHulkinZ You are not making any sense

[datHulkinZ]

wtf so bullshit in 1 plase p=180 p/4=180:4=45 why the fuck i must use my phone for this

[dustyivey89]

youre videos are the most relivent math videos i have ever seen. thank you

[CDsnuts000]

Sal Khan for president!!!!!

[dundunspaz1]

Question, when you went from A(tan(0.54))=3 to A=3/(tan(0.54)), how do you know not to use arctan, but to simply divide on thru?

[master10123]

Hey Sal when you said tan(.54) is equal to 3/5 how was that possible? in Radians tan(.54) is equal to 0.599

[PCguy102]

wouldn't using decimal values for the sides and angles be easier?

[Xkilluminati76]

cos(pi/4) is also 1/sqrt(2) [if u use the 45 triangle] Using that you would then get 10sqrt(2) * 1/sqrt(2) which is just 10

[nycgurl017]

LOL the sneeze scared me cuz I was concentrating so hard LOL

[Chigises]

Woww that was my ear :p

[garuga0777]

its easy until u put it in the calculator and it gives u a decimal

[andreiduffy]

In my country we have to memorize what sin/cos/tan/cot of 30/45/60 degrees is.

[philiiiiiiippe]

you know, you are using a drawing program... and in a drawing program, there is a "straight line" tool. :)

[shemulable]

apnake niea amra gorbo feel kori

[shemulable]

ur way of telling " excuse me " was funny but it was nice

[JRODTHEVID]

hes good but idk why he puts in all this technical pi shit with all his numbers that makes it 100% harder.

[joeman840]

wtf dude just use numbers none of the square root shit, ur suppose to be making this easier!!

[mayabooba]

what programme are you using?

[SentientRaven]

@mayabooba: He appears to use MS Paint. If you're on Windows, Click Windows-R and type "mspaint", enter.

[ooglebydoogleby]

very nice

[griefer1]

to bad all triangles arnt right triangles

[MajDigi]

@griefer1 Every triangle is at most 2 right triangles.

[affandism]

lol! u r shocking me!

im using speaker with bass

u sneeze booming me

[simsek03]

pretty cool, thanks

[vovikb50]

There is an easier way to solve this:

This is right triangle, where other angles are pi/4 (45 degrees), therefore the other angle is 45 degrees, too. Since the hypotenuse is 10sqrt2, then sides are 10.

We observe this from a square with a side of 1: the diagonal is sqrt2.

[VeniasHD]

@vovikb50 That might be easier, but someone like me, and I'm guessing many others who watched this videos, are specifically asked to show their calculations on exams using these specific cosine, sine and tangent steps.

[LouDubzENT]

my teacher gave us 3 classes of 1hour and 15 mins and i was still kinda loss i watched his vids in a half an hour and i understand ALOT better

YOU JUST OWNED MY MATH TEACHER

[GoSuMonSteR]

@LouDubzENT LOL so true.

[prence1725]

@LouDubzENT what do you think some of the teachers are missing when it comes to teaching?

[Zeldakitteh]

@LouDubzENT I would not say owned, Khan likely filled the holes from your classes.

[sandloover]

very useful :)

[aceyabank]

you're better than my teacher dude!

[LuisRC91]

@anabelbrisbane89 what? can you please explain this better? is it like a multiplication table?

[tronulu]

"OMG HE SNEEZED" get a laif noobs

[VAtidefan]

Very helpful. Thanks

[kroxish]

OMG! Did he sneeze?!

[pbbgirl4avrme]

ITS YELLOW

[crneroses]

He said highlight that side hes trying to work out in "orange"...It's yellow, or is it just me?

[semi1057]

The sneeze was hilarious.

[Kane19951996]

Excellente!

[DiXboiDeV]

i still need to kno how you got the whole square root 2 over 2, from cos, pi over 4....that confuses the hell outta me

[dija777]

Why couldn't you have just used the 45-45-90 right triangle formula from geometry? That would have been a long simpler.

[Pixelgel]

Because he is teaching trig... Is it not obvious?

[M1SSG1GGL3Z]

Thank-you so much, you helped me refresh my memory and get prepared for my aptitude testing tomorrow, complete legend, thank-you for taking the time to do this for us. Peace and happy new year!

Jaime-lee

[SKAD4LIFE86]

.599 = 6, 6=6/10=3/5 lol

[SowhatNC]

Thanks for the video and Gesundheit.

[pezimaxie]

you helped me refresh my memory

[BannedLol4l]

My calculator says tan(0.54) = 0.599429623

Why is that? (By the way, I did make sure I was in radians).

[gentlestormtoo]

Banned it depends on what quadrant your calculator is using

[washedrepent1]

@BannedLol4l you have to put your calculator in degrees in order to use hyp sin cos and tan. that the only way to make sure it shows the right value.

[tmeekins42]

He generated the problem by nicely have the sides as 3 and 5, so the angle is atan(3/5) which is 0.5404195... etc.. which he rounded to 2 significant digits: 0.54. (losing a small amount of accuracy, hence the discrepency) Since the given angle in the problem is 2 significant digits, you should only use 2 significant digits when performing the tan function on your calculator. so your 0.599429623 result rounds upwards to 0.60.

[ProjectXenon]

@BannedLol4l

You have to so the inverse: tan^-1(0.54)

[meinefresse94]

0.59942 is about 3/5. He just said about 3/5 because it was easyer to solve. if he said 0.59942 A would equal a strange number and not 10. all in all it's because it's easyer for us to understand.

[mata2001]

Thanks Sal!!

[BobMarley211]

crazy crazy

but you helped me figure it out in a diff perspective

thanks man

nice vids

[AtheismIsWiked]

ok... so you don't memorize it but how did someone figure out what a cosine is...

[ericsermon2006]

Use soh cah toa where soh is (s)in = (o)pposite divided by (h)ypotenuse; cah is (c)osine = (a)jacent divided by (h)yptenuse; and toa is (t)angent = (o)pposite over (a)jacent.

or sin = opp/hyp; cosine = aj/hyp; and tan = opp / aj

[wb678]

God bless you, Sal. I don't know what I'd do with out your videos.

[watergroovin]

Actually trig is superb in the right hands. I use Excel to get close enough approximation like if I have a rise of 3 inches of land over one mile what is the angle of slope. You may ask why that is important, well to a railroad engineer it is very important: the least slope is the least energy used, making the CEO very happy. That is an actual real life example as I know most of you think why do I need to know this. Trig can help solve global warming!

Great mnemonics!

Get excellent at Trig!

[FireBenderKwyna]

I wish you were my math teacher.

[panefuldeath]

that sneeze was funny >.>

[silentperson233]

For the first example, you can also realize it's a 45-45-90 right triangle and just divide 10 root 2 by root 2 and get 10. :)

pi / 4 = 45 degrees

In 45-45-90 right triangles, the legs are the same length, and the hypotenuse is root 2 times the leg length.

In 30-60-90 right triangles, the shortest leg is x, the other leg is x root 3, and the hypotenuse is 2x.

(just adding to the lesson) :)

[XirianValeria01]

to anyone: I'm kinda sick right now while watching the video and maybe it's just me, but please help:

how did...

tan0.54= 3 all over 3/5???

When I used my calculator, it became a decimal... :| Is it because of my sci. cal's settings??

[Corazone1983]

Your calc is set correctly.

tan(0.54rad) is roughly 0,5994296231624897545118003755­1622.

He shorted out on the explanation by not saying its rounded off and then be forced to explain how to round off etc. Probably to aviod confusion and ading 10 minutes about how to round of.

[XirianValeria01]

Oh, thank you very much! I appreciate it. :)

[pat6295]

use real nomber whats .54rad just say 45 degres

[Swiftsuper1600]

Try using single numbers cause these others confuse me?!?!?!

[joshua1auhsoj]

trig sucks...AHHHHHHHHHHH!!!!!!!

[lillyvalleys]

Does anyone know how to work this out?

I have to find the values of a and b given that

R=10

α=arctan(3/4)

Rcos(θ+α)= acosθ + bsinθ

It's been driving me bonkers! I've tried the

cos(θ+α) and substituting in different ways but just end up with a huge equation that does not make sense...

[12HOSKIT]

me to

[mrsherriff1]

thank you so much, this helped me pass my exam :D