# Cathetus and hypotenuse

Prerequisite for the Pythagorean theorem is a **right triangle**. Every right triangle always has a $90^\circ$ angle.
If the triangle does not have a right angle, none of these phrases applies.

If the requirement is fulfilled, you have to determine the **catheti** and the **hypotenuse** first:

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### Remember

- The
**hypotenuse**is the opposite side to the right angle. It is also the longest side in the triangle. **Catheti**are the other two sides that are**not**opposite to the right angle.