**Important Concepts and Formulas**

1. The distance between two points P(x

_{1}, y_{1}) and Q(x_{2}, y_{2}) is given by:
This is called the distance formula.

2. The distance of a point P(x, y) from
the origin is given by:

3. The coordinates of the point P(x, y)
which divides the line segment joining the points P(x

_{1}, y_{1}) and Q(x_{2}, y_{2}) internally in the ratio m_{1}: m_{2}are given by:
4. The mid-point of the line segment
joining the points A(x

_{1}, y_{1}) and B(x_{2}, y_{2}) is given by:
5. The area of the triangle formed by
the points A(x

_{1}, y_{1}), B(x_{2}, y_{2}) and C(x_{3}, y_{3}) is given by: