# 1.4 Describing shapes

When you are describing a geometrical figure or shape, you often need to refer to a particular line or angle on the diagram, so others know what you are referring to. This can be done by labelling the diagram with letters. For example, Figure 10 shows a triangle labelled clockwise at the corners with A,B,C. This is then known as triangle *ABC*, in which the longest side is *AB* and the angle is a right angle. is the angle formed by the lines *AC* and *CB*. The point where two lines meet is known as a **vertex** (the plural is vertices). So A, B and C are **vertices** of the triangle.

Note that you can use the shorthand notation ‘’ for ‘the triangle *ABC*’ if you wish. There is a lot of new maths vocabulary in these last few sections, so you might find it useful to make a note of these to refer back to when completing this next activity, or for this week’s quiz and the badged quiz in Week 8.

## Activity 1 What can you see?

Look at the image below and then answer the following questions using the letters shown.

- a.Which sets of lines appear to be parellel?

### Answer

a.

b.

*AB*is parallel to*DC*.*AD*is parallel to*GI*and*BC*.*AI*is parallel to*EH*.*BD*is parallel to*HJ*

- b.Which lines are perpendicular?

### Answer

b.

*AB*is perpendicular to*AD*and to*BC*.*DC*is perpendicular to*AD*and*BC*.*EH*is perpendicular to*DB*and*HJ*.*AI*is perpendicular to*HJ*and*DB*.

- c.How many triangles can you see?

### Answer

- c.

- d.What other shapes can you see?

### Answer

d.The parallelogram,

*GBJI*.The squares,

*ABCD*and*EFIH*.The trapeziums,

*DHIF*,*EHIG*,*DBJH*,*BJHE*and*DGIH*.

This completes your work on defining shapes and how to label them in order to describe them clearly to others.

The next section looks at the different ways for measuring shapes.