Right Triangles

A right triangle is a special kind of triangle. It has three sides and three corners like any triangle. But one of its corners is exactly 90 degrees. That corner is called a right angle. We often draw a small square inside that corner to show it.

Parts of a Right Triangle

A right triangle has three sides with special names. The two sides that form the right angle are called legs. The longest side is called the hypotenuse. The hypotenuse is always across from the right angle. Right triangles are used to make buildings and ramps strong.

The Pythagorean Theorem

A very old rule helps us with right triangles. It is called the Pythagorean theorem. It says the square of the hypotenuse equals the square of one leg plus the square of the other leg. This helps us find a missing side. People have used this rule for more than 2,000 years.

Fun Facts

• The smallest angle of a right triangle must be less than 90 degrees.
• A right triangle with sides 3, 4, and 5 is a famous example.
• Set squares used in art class are right triangles.

Did You Know?

Pythagoras was a Greek thinker who lived about 2,500 years ago. The famous rule about right triangles is named after him.