The Law of Cosines

The law of sines helped us solve for all the sides and angles in SAA, ASA, and SSA triangles, but now we have to learn the law of cosines if we want to solve for SAS and SSS triangles. This one is kind of like the pythagorean theorem, just for oblique triangles instead of right triangles, so it has trig functions in it. Let's check it out!

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[Clarice]

tysm! i fell asleep in class and this was our lesson for today. super helpful.

[dartheater]

I'm currently failing a test on this

[habibaelhadad]

i like your smart way of teaching professor dave

[manuellakasiama]

so if I get it right when the answer is a negative you turn it to positive like in the example where cosC =-0.157 you did cos^-1(-0157) then got a positive 99.0 and that was the final answer. am I right ?

[JM-xzur]

oh my god you literally saved me thank u sm!!!

[stevkohudran]

In the comprehension i got 77.673 as cosA while you got 75. I used the cos rule and used the sides to calculate A. How did you do it to get 75? Thanks in advance.

[manuellakasiama]

I see you've only used 2 of the formulas so how to solve with b^2=a^2+c^2-2ac cos B?

[NJ-coqs]

nice video and good graphics
how do you edit these videos 👍👌

[bravo]

At 2:49 you say "just divide". Where does division come from? Thanks. very helpful.

[cometolearn]

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[airhead]

Sometimes I don’t know the difference between sine and tangent

[abiasiddiqui]

Plz upload a video about sine and cosine of obtuse angles

[hockeyfan]

Why did you just show how to do cosine law and didn’t show how to do sine law in the first question can’t really get anywhere if I can’t figure out to to do the sine law in that specific question

[nikolaivii]

While doing the example (starts around 2m30s), it sounds like you recorded it using a different angle name, then dubbed over "C" in relevant places, and maybe cut a few bits off the original explanation. Am I right?

[estebanadrianeb.]

how did the value of a became 7.92? can you please answer i'm not good at math thank you :)

[FredrikSvensson]

You bear a slight resemblance to 66Samus, the death metal drummer. Emphasis on slight.

[mochigyu]

/2 (4.8) (6.3) howw can someone tell mee sorry i can't I'm not good at mathh

[palakmotivation]

I'm from India....but I study from this video 🤩🤩

[Belmont]

If you guys are wondering, c is 13.4, Not 13.

[josephmalone]

I get that for SSS solving the angle C first avoids ambiguity but what I don't get is why side c is on the bottom. Why is side c on the bottom? Is there a reason or just arbitrary? I want to put side b on the bottom. How does side c on the bottom help us? If it doesn't I am putting side b on the bottom unless someone smarter than me can justify this orientation. If you don't know why side c is on the bottom it is okay I just don't get it. I mean you swapped angle B and angle C and it doesn't seem instantly familiar. Is the longest side always on the bottom?