- Position of a point P in the Cartesian plane with respect to co-ordinate axes is represented by the ordered pair (x, y).

- The line X’OX is called the X-axis and YOY’ is called the Y-axis.
- The part of intersection of the X-axis and Y-axis is called the origin O and the co-ordinates of O are (0, 0).
- The perpendicular distance of a point P from the Y-axis is the ‘x’ co-ordinate and is called the abscissa.
- The perpendicular distance of a point P from the X-axis is the ‘y’ co-ordinate and is called the ordinate.
- Signs of abscissa and ordinate in different quadrants are as given in the diagram:

- Any point on the X-axis is of the form (x, 0).
- Any point on the Y-axis is of the form (0, y).
- The distance between two points P(x1, y1) and Q (x2, y2) is given by

PQ =

Note. If O is the origin, the distance of a point P(x, y) from the origin O(0, 0) is given by

OP =

**Section formula.** The coordinates of the point which divides the line segment joining the points A(x1, y1) and B(x2, y2) internally in the ratio m : n are:

The above formula is section formula. The ratio m: n can also be written as : 1 or k : 1, The

co-ordinates of P can also be written as P(x,y) =

The mid-point of the line segment joining the points P(x1, y1) and Q(x2, y2) is

Here m : n = 1 :1.

**Area of a Triangle.** The area of a triangle formed by points A(x1 y1), B(x2, y2) and C(x3, y3) is given by | ∆ |,

where ∆ =

where ∆ represents the absolute value.

- Three points are collinear if |A| = 0.
- If P is centroid of a triangle then the median divides it in the ratio 2 :1. Co-ordinates of P are given by

**Area of a quadrilateral,** ABCD = ar(∆ABC) + ar(∆ADC)