Definition
Right triangle
A right triangle is a triangle with one angle measuring exactly 90 degrees.
What it means
Find the corner that makes a perfect square corner. That corner is a right angle, so it measures 90°. The triangle can point or lean in any direction; the right-angle mark is what matters. In UK and Singapore materials, the same shape may be called a right-angled triangle.
Remember it
Spot the little square corner: it marks the triangle’s 90° angle.
Example
Cut a square from one corner to the opposite corner. Each half is a right triangle because each half keeps one of the square’s 90° corners.
Watch for
A triangle that only looks upright is not necessarily right; one angle must actually measure 90°.
Common mix-up
“Right” describes an angle, not a direction. A turned right triangle is still a right triangle.
Exact meaning
A right triangle is a triangle that has one right angle, an angle of exactly 90 degrees.