quadrilaterals

A quadrilateral is a four-sided polygon. A quadrilateral has four vertices, four angles and four sides.

• The four points A, B, C , D are the vertices of the quadrilateral ABCD.
• There are four angles:  ∠DAB, ∠ABC, ∠BCD and ∠CDA.
• The four line segments AB, BC, CD and DA are called its sides.
• AC and BD are the diagonals of the quadrilateral ABCD.

Adjacent and opposite sides: Any two sides that meet in a vertex of the quadrilateral are called its adjacent sides. Sides that do not meet in a vertex are called the opposite sides. For example:

• AB and AD are pair of adjacent sides.
• AB and DC are pair of opposite sides

Adjacent and opposite angles: Two angles of a quadrilateral are called its adjacent angles if they have a side in common. Two angles that are not adjacent are called opposite angles. For example:

• ∠A and ∠B are adjacent angles.
• ∠A and ∠C are opposite angles

Angle sum property of a quadrilateral: The sum of the measure of the interior angles of a quadrilateral is 360°, i.e. ∠A + ∠B + ∠C + ∠D = 360
 

---

Types of quadrilaterals

 

Parallelogram		A quadrilateral which has two pairs of opposite sides parallel.
Rectangle		A parallelogram whose each angle is a right angle.
Square		A square is a rectangle that has two adjacent sides equal.
Rhombus		A rhombus is a parallelogram that has two adjacents sides equal.
Kite		A kite is a quadrilateral that has two pairs of adjacent sides equal.
Trapezium		A trapezium is a quadrilateral that has a pair of opposite sides parallel but the other two sides are non-parallel.
Isosceles Trapezium		If the two non-parallel sides of a trapezium are equal then it is called an isosceles trapezium.