Triangles are polygons with three sides.
Angle Properties of Triangles
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The interior angles of a triangle always add up to 180°. ( ∠ sum of Δ) |
a + b + c = 180°
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An exterior angle of a triangle is equal to the sum of the two opposite interior angles. (ext. ∠ of Δ = sum of int.opp ∠s) |
w = x + y
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The exterior angles of a triangle always add up to 360°. (sum of ext. ∠s of Δ)
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m + n + p = 360°
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The smallest angle of a triangle is opposite the smallest side.
The largest angle of a triangle is opposite the largest side.
Types of Triangles
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An acute − angled triangle contains no angles greater than 90°
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∠A , ∠B and ∠C are all acute angles.
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A right − angled triangle contains an angle of 90°.
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∠A = 90°
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| An obtuse − angled triangle contains an angle between 90°and 180°. | ∠A is an obtuse angle |
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An isosceles triangle has one axis of symmetry. An isosceles triangle has two equal sides and two equal angles. |
sides: a = b
angles: ∠A =∠B |
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An equilateral triangle is one in which all three sides are of equal length and each interior angle is 60°. An equilateral triangle has three axes of symmetry.
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sides: a = b = c angles: |
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