Pythagorean identities

• This important identity can be derived as a direct result of Pythagoras's theorem, when applied to angles in trigonometry:
• sin²x + cos²x = 1 (1)
• By dividing each of these terms by sin²x, we can derive a second identity:
• 1 + cot²x = cosec²x
• By dividing (1) by cos²x, we arrive at the third (and final) identity:
• tan²x + 1 = sec²x