## Proofs for Standard Results |

## sin

^{2}θ + cos^{2}θ = 1

If one is using a power series approach to define cos and sin this result follows immeadiately, however, if instead one is taking a triangle approach then the proof is as follows:

It's clear that sin θ = b/c

cos θ = a/c

=> sin^{2}θ + cos^{2}θ = (a^{2}+ b^{2})/c^{2}= 1 by Pythagorus (a^{2}+ b^{2}= c^{2}).

©Neil Roques 2004

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