Theorem 8.8 Class 9 A Quadrilateral is a parallelogram if a pair of opposite sides are equal and parallel.

- Theorem 8.1 A Diagonals of a parallelogram divides it into two congruent triangles.
- Theorem 8.2 In a parallelogram, opposite sides are equal.
- Theorem 8.3 If each pair of opposite sides of a quadrilateral is equal, then it is a parallelogram.
- Theorem 8.4 In a parallelogram, opposite angles are equal.
- Theorem 8.5 If in a Quadrilateral, each pair of opposite angles is equal, then it is a parallelogram.
- Theorem 8.6 The diagonals of a parallelogram bisect each other.
- Theorem 8.7 If the diagonals of a Quadrilateral bisect each other, then it is a parallelogram.
- Theorem 8.8 A Quadrilateral is a parallelogram if a pair of opposite sides are equal and parallel.
- Theorem 8.9 The line segment joining the mid-points of two sides of a triangle is parallel to the third side.
- Theorem 8.10 The line drawn through the mid-point of one side of a triangle, parallel to another side bisects the third side.