- Angle Sum Property of a Quadrilateral
- Types of Quadrilaterals
- Properties of a Parallelogram
- The Mid-Point Theorem
- Sum of the angles of a quadrilateral is 360^{o}
- A diagonals of a parallelogram divides it into two congruent triangles.
- In a parallelogram
- diagonals bisect each other.
- opposite angles are equal.
- opposite sides are equal
- Diagonals of a square bisects each other at right angles and are equal, and vice-versa.
- A line through the mid-point of a side of a triangle parallel to another side bisects the third side. (mid-point theorem)
- The line through the mid points of sides of a D || to third side and half of it.
- A quadrilateral is a parallelogram, if
- its opposite angles are equal.
- its opposite sides are equal.
- its diagonals bisect each other.
- a pair of opposite sides is equal and parallel.
- Diagonals of a rectangle bisect each other and are equal and vice-versa.
- Diagonals of a rhombus bisect each other at right angles and vice-versa.
- A line through the mid-point of a side of a triangle parallel to another side bisects the third side.
- 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.