Quadrilaterals - ESSENTIAL POINTS
- A quadrilateral has four sides, four angles and four vertices.
- The sum of all the angles of a quadrilateral is 360°.
- Types of Quadrilaterals:
- Parallelogram - A quadrilateralthat has both pairs of opposite sides parallel. It is a trapezium.
- Rectangle – A parallelogramthat has one of its angles a right angle.
- Rhombus - A parallelogram that has all its sides equal.
- Square - A parallelogram that has one of its angles a right angle and all sides equal. It is a rectangle and also a rhombus.
- Trapezium - One pair of opposite sides of quadrilateral are parallel. It is not a parallelogramas only one pair of opposite sides is parallel.
- Kite - A quadrilateral that has two pairs of adjacent sides equal. It is not a parallelogram.
- A rectangle or a rhombus is not a square.
- In a parallelogram:
- diagonal divides it into two congruent triangles
- opposite sides are equal
- pair of opposite sides is equal and parallel
- opposite angles are equal
- each pair of opposite angles is equal
- diagonals bisect each other
- Diagonals of a rectangle bisect each other and are equal.
- Diagonals of a rhombus bisect each other at right angles.
- Diagonals of a square bisect each other at right angles and are equal.
- 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.
- A line through the mid-point of a side of a triangle parallel to another side bisects the third side.
- The quadrilateral formed by joining the mid-points of the sides of a quadrilateral, taken in order, is a parallelogram.
