# Chapter 8 Quadrilaterals Notes for Class 9th Maths

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• Angle Sum Property of a Quadrilateral
• Properties of a Parallelogram
• The Mid-Point Theorem
1. Sum of the angles of a quadrilateral is 360o
2. A diagonals of a parallelogram divides it into two congruent triangles.
3. In a parallelogram
4. diagonals bisect each other.
5. opposite angles are equal.
6. opposite sides are equal
7. Diagonals of a square bisects each other at right angles and are equal, and vice-versa.
8. A line through the mid-point of a side of a triangle parallel to another side bisects the third side. (mid-point theorem)
9. The line through the mid points of sides of a D || to third side and half of it.
10. A quadrilateral is a parallelogram, if
11. its opposite angles are equal.
12. its opposite sides are equal.
13. its diagonals bisect each other.
14. a pair of opposite sides is equal and parallel.
15. Diagonals of a rectangle bisect each other and are equal and vice-versa.
16. Diagonals of a rhombus bisect each other at right angles and vice-versa.
17. A line through the mid-point of a side of a triangle parallel to another side bisects the third side.
18. 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.