Right Angle
A right angle is an angle measuring exactly 90°. Right angles are mathematically significant to topics such as geometry and trigonometry.
A most common form of a right angle, or 90° angle, includes two perpendicular lines meeting at an apex. This forms a perfect ‘L’ or corner shape.
Right angles are represented with a square, unlike those depicted in Mathematics with a curved line. Knowing that one angle is a right angle can allow Maths students to calculate different angles within a shape.
Why is a 90° angle called a Right Angle?
The name comes from the fact that when two straight lines intersect, they form two angles. If the two angles are equal, this is a ‘just’ or ‘right’ situation. Hence, they’re referred to as ‘right’ angles. In ancient geometry, ‘right’ also refers to the fact that two straight lines form them.
Right Angles in Angles and Trigonometry
Right angles are an essential feature in several Maths topics. For example, knowing how many degrees are in a right angle can help your class when finding and calculating missing angle questions.
For instance, the interior angles of a quadrilateral always equal 360° while the interior angles of a triangle always equal 180°. With this knowledge, your KS1 Maths students can estimate and calculate the remaining angles if they know that one or more are right angles.
Right angles are also used throughout a child’s learning journey and have many real-life applications. For example, you wouldn’t want the edges of a door or window to be anything other than a 90° angle!
How to Measure a Right Angle
If right angles are not marked on a Maths problem or worksheet, your students may need to measure them by hand.
This must be done with either a 180 or 360 protractor. This mathematical instrument measures angles, generally made from transparent plastic or glass. Some even have moving parts to make the measuring process more accessible.
Protractor skills are valuable in the study of Maths. To measure a right angle, students must line up the axis of the protractor with the apex of the two connecting lines of an angle.
- If the measurement equals 90°, then this is a right angle.
- If the angle exceeds 90°, it is an obtuse angle.
- If the angle is less than 90°, it is acute.
- If the angle exceeds 180°, then it is a reflex angle.
- If the angle is exactly equal to 180°, then it is a straight angle or half-turn.
