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# pythagorean identities - method for remembering em watch

1. Everyone probably knows this already, but Dad just told me it and I think it’s a neat way of remembering the Pythagorean identities.

Taking a right-angled triangle, and using θ as the angle, b as the opposite side, a as the adjacent side and c as the hypotenuse, you have, using Pythagoras:

a2 + b2 = c2

dividing through by a2 you get

1 + tan2 θ = sec2 θ

dividing through by b2 you get

cot2 θ + 1 = cos2 θ

and dividing through by c2 you get

sin2 θ + cos2 θ = 1

Which I think is a beautifully simple way of remembering these equations.
2. Nice one

And not a moment too soon....

I wish my parents knew what pythagorean identities were
3. (Original post by lesser weevil)

dividing through by b2 you get

cot2 θ + 1 = cos2 θ
almost fine but should be cosec²x

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