Lines and angles

What is a line?

A line is a straight object which has no width and extends forever in both directions. Lines are sometimes drawn with arrows at both ends to show that they go on forever. Look at the symbol of a line below.

Now look at the picture below. It shows two lines which are the same distance apart along their entire length. They are called parallel lines. Parallel lines will never meet or cross no matter how far they are extended.

Look at the lines below. They are known as perpendicular lines. Perpendicular lines meet or cross over each other at a ninety degree angle. Ninety degree angles are also known as right angles. Therefore we can also say that perpendicular lines meet or cross each other at right angles. The letter T is a good example of perpendicular lines.

Note: Often in Mathematics we work with a part of a line which has two end points. This is known as a line segment.

Angles

What is an angle?

When two lines or line segments meet at a point, an angle is formed. The point at which two lines meet is called the vertex. An angle can be defined as the amount of turn between two lines and the vertex. The word angle is derived from a word which means corner. So you can think of an angle as the little corner that forms where two lines meet.

Measuring Angles

Angles can be many different sizes. The size of an angle is measured in degrees. A protractor can be used to measure the size of an angle. Look at the picture of the protractor below.

To measure the size of an angle, ensure the middle point of the line at the bottom of the protractor is at the vertex of the angle. The base line of the protractor should be placed on one of the lines that forms the angle. Find where the second line lies along the protractor. Read the size of the angle by going from zero to the point where the second line is found. Look at the picture below. A protractor is being used to measure the size of an angle. Can you tell the size of the angle?