Right triangle facts for kids

A right triangle has one angle that is exactly 90 degrees.

A right triangle is a special kind of triangle. It has one angle that measures exactly 90 degrees. This 90-degree angle is also called a right angle.

The other two angles in a right triangle always add up to 90 degrees. For example, if one angle is 30 degrees, the other must be 60 degrees. This is because all the angles inside any triangle always add up to 180 degrees.

Parts of a Right Triangle

Every right triangle has three sides and three angles. The sides have special names:

• The hypotenuse is the longest side. It is always found directly across from the 90-degree angle.
• The other two sides are called legs. These two sides form the 90-degree angle. Sometimes, they are also called "catheti" (singular: cathetus).

Finding Missing Sides and Angles

If you know some parts of a right triangle, you can figure out the missing ones!

• The Pythagorean theorem is a famous rule that helps you find the length of a missing side. It says that if 'a' and 'b' are the lengths of the legs, and 'c' is the length of the hypotenuse, then a² + b² = c².
• Trigonometry is a branch of math that uses special ratios (like sine, cosine, and tangent) to find missing angles or sides when you know at least one side and one angle (besides the right angle).

Images for kids

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  Altitude of a right triangle

See also

In Spanish: Triángulo rectángulo para niños