Trig identities part 2 (parr 4 if you watch the proofs)

[koolcorner008]

can u please improve the quality of the videos..thanks :)

[RomansRevenge123]

I get to school and hear teachers talk about *_*....then i get to youtube and itss like..wow i learned smethin new today...^_^

[sweetstrwberry1]

at 6:52 why is it 2sinacosa, isnt suppose to be 2sinacosb? sorry if i dont get itXD

[tedward191]

good not having heads in the way

[100redeye]

functions test hero

[hotvampire1992]

Those 8 dislikes are by teachers :P

[hgbpo]

@MrTeeson thanks :)

[HypeeTommy]

You suck tyson.

[hgbpo]

how come when you're proving the cos(2a) identity, the sines suddenly become negative?

[MrTeeson]

@hgbpo its part of the double angle formula (cos2a) = cos^2a - sin^2x :)

[soulestazn]

@MrTeeson that is incorrect my friend. cos2a = cos^2 a - sin^2 a

[MrTeeson]

@soulestazn lol...

[HypeeTommy]

@MrTeeson 96 ATAR

[MrTeeson]

@HypeeTommy cheayea xD

[ItsJonYo]

@hgbpo Well as you see cos (2a) = cos (a+b) as shown in the vid. Where you end up with cos^2a- sin^2a.

Your asking why is it -sin^2a, well thats how the formula is given to cos(a+b). 8:06.

[jeffaschwarz]

Around 1:20 you seem confused about why there is a secant and cosecant. The reason for that is because raising sine and cosine to the negative first power (sin^-1 or cos^-1), which would normally represent 1/sin and 1/cos, are used instead to indicate the inverse functions arcsine and arccosine.

[harr1s0n2]

you sound like seananners that does the call of duty commentaries

[earlysauce]

Lol..... ChoShaTao

[TheBobbyTheCamel]

Your title is spelled wrong.

[SuperBarbiel]

thanks a million ... u saved my life

[SuperBarbiel]

ur a life saver trust me ... where u frm??

[dycarbon1]

Where are your other two proof videos? =(

[Rohan42153]

thank you! i love you man no homo this saved my life on the mid terms

[WiserRS]

You ARE AMAZING! I never thought i'd understand trigonemtry, but i mean OMFG! I finally do because of you. I can do like everyother mathametical type problem, but trig was just a pain in the damn ass. I've seen the light. I got an A on my test, tysm! All i can do to help is sub =/

[toolbass24]

ur awesome man. u dont know how many people uve helped nail this subject. im learning right now. i have a test in a few days and thanks to you im going to pass :) god bless

[DawnBreaker1100]

Definitional?

[pyLz]

you could even add cos²a+sin²a to cos²a-sin²a, which results in cos(2a)+1 = 2cos²(a) :D

[kungfufreak360]

How awesome would Khan Academy be of it was in HD!

[malubayraymond]

thank you sir, you know ABSOLUTELY everything.

[heineken1122]

I really like your videos. They explain things ALOT better than any maths teacher i've had. Thank you!

[gabbnics]

i really like all your videos..:)

[IamBored529]

I dont thnk I cud ever make it through high school if it werent for you

[GreenFear]

You are better than any math teacher I have ever had lol and I'm in a University.

[ericxmarcelo]

I almost a 90% sure my math teacher watch your videos before teaching us, he says kind of the same stuff similar words and what not, but since is a simple topic probably is just casuality.

[bellatesla]

I almost a good in English

[aidanpugh]

that's pretty funny

[EmanSaraNermein]

seriously thank u very muchhhhh

[edklinger]

i never knew forest gump was so good at maths

[d0ntl4ugh]

he doesnt sound like forrest gump at all you sad fuck

[GangstaGriIIz]

youtube > teachers

[IamBored529]

@GangstaGriIIz I agree completely

[Celestialbeing21]

@GangstaGriIIz

as sad as it is too say. Textbooks don't really efficiently walk you through these formulas by repeating the basics then to the complex. They fail at khanacademy's logic.

[damthatriver09]

@GangstaGriIIz Yeah we should abolish grade school and learn from sal.

[brandonsuji]

@GangstaGriIIz so true dude

[Winsunn307]

Thank you for these videos. I don't really understand them, yet, but I will. You are a great help to me.

[perezallonzo]

you really help me and the way you teach is very enjoyable considering that i am in pre alg.

[ajithla]

you are doing a very nice job

it really helped me alot

[opinionhead444]

I like these videos. Have you considered doing a series on the "extinct" trig functions like versine and exsecant?

Might be interesting.

[khanacademy]

That's interesting. I actually didn't know about them. I read about them after your comment. I might do some videos on this.

[itsaidhi]

@khanacademy

did you ever do any?

[mrhnm]

@khanacademy My buddy actually used versine to prove a formula on a test in one of his calculus classes. He forgot what he was supposed to have memorized and ended up having to derive it.

[lazmedina]

Where was YouTube when I was in High School?

Kids have it so easy these days. Well of course not all kids, the digital divide is prevelant in so many parts of the world-it isn't even fair that these kids will have to compete against us.

[UnrecycleRubdish]

@lazmedina I am replying to an old comment but the argument is still relevant. It's not fair? Instead of being happy that people are being educated more easily, you say it isn't fair? That's ignorant and arrogant. It's a good thing no matter how you look at it.

[system0slaven]

soh cah toa

LOL

[cbalili91]

how would u prove (sin0)(tan0)+ cos0=sec0

(sin0) x (sin0/cos0) + cos0/1 ?

[igor31]

that is (sin^2(0)/cos(0))+(cos^2(0)/co­s(0))=1/(cos(0)) that is ((sin^2(0))+(cos^2(0)))/cos(0)­=1/(cos(0)) because sin^2(0)+cos^2(0)=1 there it is. ^2 means squared,i hate that notation