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