A line is the Set of infinite points which join together to form the line. A line extends in both the directions and so we say that it has no fixed length. When we say that two given lines are

**perpendicular lines**it means that the two lines make the angle of 90 degree with each other.
Some real life examples of perpendicular lines are given below:

- If we look at the English alphabets, we observe that alphabet T, L, H is the examples of the perpendicular lines.
- When we see the clock struck 9, it means that the hour hand is on 9 and the minute hand is at 12, at this situation, the two hands of the clock are perpendicular to each other.
- If we look at the adjacent sides of the window panes, they are perpendicular to each other.
- Adjacent sides of the table and adjacent walls with their edges make an angle of 90 degrees with each other so we also say that they are perpendicular to each other.

If two perpendicular lines are joined together, it forms an angle of 90 + 90 degrees i.e. 180 degree. Here we notice that an angle of the Straight Line is 180 degrees, so we say that they form together a straight line. Also if two angles join together to form the straight line, we call them a linear pair of lines. It directly indicates that the two pair of perpendicular line is called linear pair.

Also we know that the pair of angles is supplementary, if their sum angle is 180 degrees. So we say that if two perpendicular lines join together, is also forms a pair of

**perpendicular lines**. If we divide a Circle in four equal parts, we observe that each of its part, which is $\frac{1}{4}$ of the total measure of 360 degrees, comes out to be 90 degrees. Thus we say that the each quadrant forms the angle of 90 degrees.