QUADRILATERALS

     QUADRILATERALS।   
THEOREMS:
1-The sum of all angles of a quadrilateral is 360.
2-A diagonal of a parallelogram divides it into two triangles of equal area.
3-In a parallelogram, opposite sides are equal.
4-The opposite angles of a parallelogram are equal.
5-The diagonals of a parallelogram bisect each other.
6-A quadrilateral is a parallelogram if its opposite sides are equal.
7-A quadrilateral is a parallelogram if its opposite angles are equal.
8-A quadrilateral is a parallelogram if its diagonals bisect each other.
9-A quadrilateral is a parallelogram if it’s one pair of opposite sides is equal and parallel.