How to Use the Pythagorean Theorem
The Pythagorean theorem says that for a right triangle with legs a and b and hypotenuse c, a² + b² = c².
When to use it
Only when you have a right angle. The hypotenuse is opposite that right angle and is the longest side.
Step-by-step method
- Identify the hypotenuse.
- Square the two known sides.
- Add or subtract according to which side is missing, then take a square root.
Example
legs 3 and 4
- 9 + 16 = 25
- c = 5
Answer: 5
Interactive example
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Example problems
Common mistakes
Squaring after adding
Square first, then add. (3+4)² is not 3²+4².
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Frequently asked questions
Does 5-12-13 work?
Yes. 25+144=169. It is a common Pythagorean triple.