Right Triangles
(KS3, Year 7)
Dictionary Definition
The Oxford English Dictionary defines a right triangle as "a triangle containing a right angle."The Parts of a Right Triangle
- A right triangle has one right angle (an angle of 90°). It is shown by drawing a small square.
- The longest side (opposite the right angle) is called the hypotenuse.
- The other two shorter sides are called legs or catheti (singular cathetus). They are perpendicular to each other.
- If another angle is labelled (such as the angle labelled θ in the image below) then we can name the two shorter sides. The side next to the angle is called the adjacent. The side opposite the angle is called the opposite.Note: The adjacent and opposite only exist in relation to an angle. The same side can be an adjacent or an opposite depending on which angle they refer to.
What's in a Name?
A right triangle gets its name from the fact it has a right angle - an angle of 90°. The right triangle is called a right-angled triangle in British English.The Other Angles in a Right Triangle
The 3 angles in a triangle must add to 180°. If one angle is 90°, the other two angles must add to 90°.Worksheet
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