Quadrilaterals- a simple closed figure surrounded by four line segment is called a quadrilaterals. It has four sides , four angles, four vertices and two diagonals. The sum of all angles are 
.
Adjacent side- having a common end point. e.g PQ & QR
Opposite side- do not have any common point. eg. PQ, RS
Similarly the adjacent angles opposite angle.
The sum of the angle of a quadrilateral is .
Type of quadrilaterals:
Rectangle– a quadrilateral in which opposite side are parallel & equal & each angle is 
called a rectangle.
Square– a rectangle in which all sides are equal opposite side are, parallel and each angle is , called a square.
Parallelogram– a quadrilateral opposite sides are parallel & opposite angles are equal is called parallelogram.
or 
(diagonals)
Rhombus– a quadrilateral which all side are equal , opposite side are parallel and opposite angles are equal is called rhombus.
Trapezium– a quadrilateral having one opposite side is parallel is called trapezium. When if its non parallel sides are equal is called isosceles trapezium. a quadrilateral is called if their adjacent sides are equal and opposite sides are unequal.
Trapezoid:
