What Are Right Triangles?

Right triangles have one right angle

Right triangles have exactly one right angle, which forms the angle with the largest measure in the triangle. Right triangles also have a hypotenuse, which is the longest side in the triangle and is always opposite the right angle.

All the triangles in the image below are right triangles.

If you know the lengths of two of a right triangle's sides, you can find the length of the third side by using the Pythagorean Theorem.

Just like in all triangles, all the angles in a right triangle add up to $180^\circ$. Since the right angle measures $90^\circ$, the other two angles also have to add up to $90^\circ$: they are complementary!