Meaning & use
right triangle
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Meaning
nouncountablemathematics
A triangle that has one angle of exactly 90 degrees.
Grammar: Countable; use 'a right triangle' for one and 'right triangles' for more than one.
Patterns
- a right triangle
- the legs of a right triangle
- draw a right triangle
The teacher asked us to draw a right triangle with sides of 3, 4, and 5 centimeters.
In a right triangle, the side opposite the right angle is called the hypotenuse.
You can use the Pythagorean theorem to find a missing side of a right triangle.
Word forms
| plural | right triangles |
|---|
Common combinations
- a right triangle with sides
- She drew a right triangle with sides of 6 and 8 centimeters.
- the legs of a right triangle
- The two shorter sides are the legs of a right triangle.
- solve a right triangle
- In trigonometry, you often solve a right triangle using sine and cosine.
- a right triangle has a 90-degree angle
- By definition, a right triangle has a 90-degree angle.
Synonyms and how they differ
- right-angled triangle
- The usual British term for the same shape; use it in British contexts.
Word family
- right angle noun
- An angle of 90 degrees.
- right-angled adjective
- Having a right angle, as in a right-angled triangle.
Commonly confused: right triangle or rectangle?
right triangle vs rectangle
A rectangle has four right angles; a right triangle has only one.
Practice
Which statement is true about a right triangle?
Choose one answer.
By definition, a right triangle has exactly one 90-degree angle. Three equal sides describes an equilateral triangle, and two right angles would make the third angle zero, which is impossible in a triangle.
Make it your own
Write a sentence using “right triangle”, then check it and compare it with the examples above.