CBSE Class 9 Mathematics/ Quadrilaterals – Chapter 8
Important points to remember:

• A four sided polygon is called a Quadrilateral.
*A quadrilateral has 4 sides, 4 angles and 4 vertices.
• Sum of the angles of a quadrilateral is 360 degree.
• In a parallelogram,
i) Opposite sides are equal.
ii) Opposite angles are equal.
iii) Diagonals bisect each other.
iv) A diagonal of a parallelogram divides it into two congruent triangles.
*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.
*Diagonals of a square bisect each other at right angles and are equal, and vice-versa.
*In a square,
i) All sides are equal
ii) All angles are 90 degree.
iii) Diagonals are equal
iv) Diagonals bisect each other at right angles.
*In a Rectangle,
i) Each angle is 90 degree
ii) Diagonals are equal
*In a rhombus,
i) All sides are equal
ii) Diagonals bisect each other at right angle
*In a trapezium,
i) Only one pair of opposite sides is parallel.
ii) Trapezium is not a parallelogram
*In a kite,
i) Two pairs of adjacent sides are equal
ii) Kite is not a parallelogram
*The quadrilateral formed by joining the mid-points of the sides of a quadrilateral, in order, is a parallelogram.
*Square, rectangle and rhombus are all parallelograms.
*A square is a rectangle and also a rhombus.
*A parallelogram is a trapezium.
*The line segment joining the mid-points of two sides of a triangle is parallel to the third side.