Pythagorean Identities
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This important identity can be derived as a direct result of Pythagoras's theorem, when applied to angles in trigonometry:

sin˛x + cos˛x = 1         (1)

By dividing each of these terms by sin˛x, we can derive a second identity:

1 + cot˛x = cosec˛x

By dividing (1) by cos˛x, we arrive at the third (and final) identity:

tan˛x + 1 = sec˛x

© Matthew Pinkey

Other Notes in this Category

1. Double angle formulae
2. Pythagorean Identities
3. Radians
4. Sec, cosec, cot
5. Sin, Cos, Tan
6. Sine and Cosine Formulae
7. Solving Trigonometric Equations

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