Proof of angle addition formula for sine | Trigonometry | Khan Academy

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[Ariana-rljr]

Loved every time he said you should be getting excited

[putzak]

Thanks my friend, you're getting me through uni 👌

[MinhTran-wnri]

Shouldn't you justify the construction of the diagram (@ 3:19) before going through the proof so that your reasoning doesn't appear to have come from observing the construction but rather from definitions? 

[suhasthegreat]

CAN anyone please tell me how AD is equal to 1, what if other values are taken??

[skeletonrowdie]

6:45 SO THAT'S WHY!
hehe. Great video thanks! always wondered about this property

[amyb]

3:42 I thought he was gna say so assuming you gave up ...

[OswaldGaming]

sal is the best teacher like if you agree

[noebarajas]

Will sin(x+y) always form 90 degree triangles that are stacked on top of each other or could the two triangles rest on the x axis?

[amyb]

Literally all I saw in class was this irregular drawing and came here now I get it bless up

[abdelhakimlamnaouar]

but what if the length of AD was not 1?

[adityaadit]

Oh mo gosh that was sooo easy thank you for enlightening my mind Mr. Sal

[datpham]

Love every time he said you might want to try it .

[asdrty]

From fig 0:17 trigonometrically >
Sinxcosy + cosxsiny
( ed=sinxcosy and ef=cosysiny)

[gosiajaneczko]

How woudl proof of x+y>90 degrees look like?

[masicbemester]

I've been wondering how and why the formula works and now I know and I wonder what the complex number proof of this would be.

[withbirds]

not sure if anyone will get back to me in time-but why do we make this diagram

[thomasbates]

Oh no. I have only watched the first 30 seconds but I think this video is going to explain to me something I was trying to understand through hours of reading. I'll reply to myself with an update if this does in fact take place.

[Kino-Imsureq]

i have been trying to figure out how to multiply lengths so you get the length of the product and then trying to use euclidean geometrical proof to do this and then i see this proof.

[ramyhuber]

Wonderful clear explanation, thank you!

[dvanielwright]

this hypothenus from side AD, is that equal to 1 because it is on a unit circle?