Constructions: compass and protractor

Using a compass and protractor to draw circles, angles, perpendicular and parallel lines, bisect lines and build triangles. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

Know it already? Jump straight to the quiz

Your progress0 of 2

Constructions

With a compass you draw circles and arcs with a fixed radius.
With a protractor you measure and draw angles.
Draw a circle with radius 3 cm: open the compass to 3 cm, put the point on the centre and turn it once all the way round.

Tap when you could tell someone without looking.

Step by step

Construction	Steps
an angle of 65°	Draw one arm. Put the centre of the protractor on the vertex with 0 on the arm. Mark 65 on the scale that starts at 0, and join the mark to the vertex.
perpendicular bisector (bisect a line)	Open the compass to more than half the line. Keep the same opening and draw an arc above and below the line from each end point. Join the two points where the arcs cross.
perpendicular line through a point on a line	Put the protractor (or a set square) on the line at the point, mark 90° and draw the line through the point.
parallel line	Draw two perpendicular lines of the same length on the first line and join their ends; or slide a set square along a ruler.
equilateral triangle	Draw the base. Open the compass as wide as the base and draw an arc from each end point. Join the point where the arcs cross to both end points.

Meerkat tip

Don’t change the compass opening between the two arcs: that is the secret of an accurate construction.

Tap when you could tell someone without looking.

Remember this and test yourself

Remember this: your summary

Compass: circles and arcs.
Protractor: measure and draw angles.
A perpendicular bisector halves a line at 90°.
Perpendicular: at 90°; parallel lines: always the same distance apart.
Keep the compass opening the same for both arcs.

Write these points in your book. Read them again the night before the test.

Memory trick

The compass remembers the distance for you.

Flash cards · Tap to turn over

Important words

First say the answer yourself, then turn the card over.

Test yourself · Part 2

True or false?

Read the question and the answer. Is the answer right? Tap True or False.

Now the real quiz!

The quiz has many more questions on this topic. Every question shows straight away whether you are right and explains why.

Take the quiz: Constructions: compass and protractor

Practise it step by step: Extra Maths Class All Grade 7 Maths summaries

For parents

Let your child work the examples on paper and explain them to you.
The ticks (“I know this”) are saved on this device only. We never ask for names or emails.

Follows CAPS for Grade 7 Mathematics. Always check your teacher’s notes and textbook too.