Triangles are polygons with three sides.
- A right − angled triangle contains an angle of 90°.
e.g. A = 90o
- An obtuse − angled triangle contains an angle between 90°and 180°.
- A scalene triangle contains three sides unequal in length. All angle sizes are different.
- An isosceles triangle is one in which two of the sides and their opposite angles are equal.
Symmetry of Triangles
An isosceles triangle has one axis of symmetry.
axis of symmetry
e.g. sides: a = b
angles: A = B
An equilateral triangle is one in which all three sides are of equal length and each interior angle is 60°.
An equilateral traingle has three axes of symmetry.
e.g. sides: a = b = c
Properties of Triangles
- The interior angles of a triangle always add up to 180°.
- An exterior angle of a triangle is equal to the sum of the two opposite interior angles.
- The exterior angles of a triangle always add up to 360°.
- The smallest angle of a triangle is opposite the smallest side.
- The largest angle of a triangle is opposite the largest side.
w = x + y
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