# The coolest fact in trigonometry that you learn way too late....

by Femme_physics
Tags: coolest, fact, late, learn, trigonometry
 PF Gold P: 2,551 So I just spent the last 12 hours learning trig (occasional food breaks). I just want to share with you something really, really, really, really, awesome. Check this out, you're gonna be blown away The law of cosines, applied to a right triangle is c^2 = a^2+b^2 - 2abCosA Whereas A is equal to zero!!! So the law of cosines for a right triangle is, in fact, the Pythagorean theorm!!! Math is sooooooooo awesome. Why did it only take me the last quarter of the textbook to learn this fact???
 HW Helper P: 1,334 Perhaps I'm missing something here, but if A = 0, cos A = 1, and your statement comes in as $$c^2 = a^2 + b^2 - 2ab$$ which is not the Pythagorean Theorem.
 PF Gold P: 2,551 I mean, A is 90 degrees and therefor 0 is equal to 0!!! Sorry
P: 22

## The coolest fact in trigonometry that you learn way too late....

 Quote by Dory Check this out, you're gonna be blown away The law of cosines, applied to a right triangle is c^2 = a^2+b^2 - 2abCosA Whereas A is equal to zero!!! So the law of cosines for a right triangle is, in fact, the Pythagorean theorm!!! Math is sooooooooo awesome. Why did it only take me the last quarter of the textbook to learn this fact???

yep it's awesome
Emeritus
PF Gold
P: 16,101
 Quote by statdad Perhaps I'm missing something here, but if A = 0, cos A = 1, and your statement comes in as $$c^2 = a^2 + b^2 - 2ab$$ which is not the Pythagorean Theorem.
Of course, this value is interesting too, as it's the theorem that if you have three collinear points:
A --- B ---- C
Then the length of the whole (b) is the sum of the lengths of the two parts (a and c).
HW Helper
P: 1,334
 Quote by Dory I mean, A is 90 degrees and therefor 0 is equal to 0!!! Sorry
Don't worry - I had a feeling this is what you meant - but I wanted to make sure.

You'll find lots of cool things in your math classes if you take the time to look around.
Mentor
P: 20,449
 Quote by Dory I mean, A is 90 degrees and therefor 0 is equal to 0!!!
You don't need the law of cosines to conclude 0 = 0.
 P: 2,258
 PF Gold P: 2,551 Awesome link granpa! And thanks for the replies and humoring me :)

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