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| Summary |
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 In a polygon of 'n' sides, the sum of the interior angles is equal to (2n - 4) right angles. |
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Each interior angle of a regular polygon is  |
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If the sides of a convex polygon are produced, in order, the sum of the exterior angles is 4 right angles. |
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Each exterior angle of a regular polygon of n sides =  |
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The opposite sides and angles of a parallelogram are equal. |
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The diagonals of a parallelogram bisect each other. |
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If a pair of opposite sides of a quadrilateral is equal and parallel, it is a parallelogram. |
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In a rectangle each angle is 90o. |
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In a rhombus all the sides are equal. The diagonals bisect each other at right angles. The diagonals bisect the angles of the rhombus. |
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If the diagonals of a parallelogram are at right angles, it is a rhombus. |
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Some special constructions: |
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| 1. Construction of Parallelograms when |
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| (a) Two sides and an angle are given |
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| (b) Diagonals and the angle included by them are given |
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| (c) One side, a diagonal and height are given |
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| (2) Construction of Rhombus when |
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| (a) both the diagonals are given |
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| (b) one diagonal and one side are given |
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| (3) Construction of a square |
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| (4) Construction of a Rectangle |
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| (5) Construction of a Regular Hexagon |
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| (6) Construction of a Regular Pentagon. |
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