Key Points - Quadrilaterals

- Angle Sum Property of a Quadrilateral
- Types of Quadrilaterals
- Properties of a Parallelogram
- The Mid-Point Theorem

(1) Sum of the angles of a quadrilateral is 360 degrees
(2) A diagonals of a parallelogram divides it into two congruent triangles.
(3) In a parallelogram (a) diagonals bisect each other. (b) opposite angles are equal. (c) opposite sides are equal 
(4) Diagonals of a square bisects each other at right angles and are equal. and vice-versa. 
(5) A line through the mid-point of a side of a triangle parallel to another side bisects the third side. (mid-point theorem) 
(6) The line through the mid points of sides of a ? || to third side and half of it. 
(7) A quadrilateral is a parallelogram. if (a) its opposite angles are equal. (b) its opposite sides are equal. (c) its diagonals bisect each other. (d) a pair of opposite sides is equal and parallel.
(8) Diagonals of a rectangle bisect each other and are equal and vice-versa. 
(9) Diagonals of a rhombus bisect each other at right angles and vice-versa.
(10) A line through the mid-point of a side of a triangle parallel to another side bisects the third side. 
(11) The line-segment joining the mid-points of any two sides of a triangle is parallel to the third side and is half of it.