Triangles
A triangle has three sides and three angles
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The three angles always add to 180°
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Equilateral, Isosceles and Scalene
There are three special names given to triangles that tell how many sides (or angles) are equal.
There can be 3, 2 or no equal sides/angles:
There can be 3, 2 or no equal sides/angles:
Equilateral TriangleThree equal sidesThree equal angles, always 60° | |
Isosceles TriangleTwo equal sidesTwo equal angles | |
Scalene TriangleNo equal sidesNo equal angles |
How to remember? Alphabetically they go 3, 2, none:
- Equilateral: "equal"-lateral (lateral means side) so they have all equal sides
- Isosceles: means "equal legs", and we have two legs, right?
Also iSOSceles has two equal "Sides" joined by an "Odd" side. - Scalene: means "uneven" or "odd", so no equal sides.
What Type of Angle?
Triangles can also have names that tell you what type of angle is inside:
Acute TriangleAll angles are less than 90° | |
Right TriangleHas a right angle (90°) | |
Obtuse TriangleHas an angle more than 90° |
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