Geometry

Triangles

• A scalene triangle has 3 sides of different lengths and 3 unequal angles.
• An isosceles triangle has 2 sides of equal length. The dashes on the lines show they are equal in length. The angles at the base of the equal sides are equal.
• An equilateral triangle has 3 sides of equal length. The dashes on the lines show they are equal in length. All of the angles are also equal.
• A right-angled triangle is a triangle that has a right angle.
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Labelling angles and sides

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• Letters can be used to label angles.
• AB and AC are line segments, and they meet at point A. AB joins the points A and B.
• The angle between AB and AC is labelled BAC.
• The angle can written as BAC or BÂC or ∠BAC.

Interior and exterior angles

• The angles inside a shape are called interior angles.
• If the side of a triangle is extended, the angle formed outside the triangle is the exterior angle.
• g is the interior angle. h is the exterior angle.
• The interior angle and its corresponding exterior angle always add up to 180°.
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