17.3 Constructions with ruler and compasses — Practise with help
Attempt each item before opening its help. Recall ideas from earlier chapters first.
Warm-up: remember
Answer these from memory. Do not look back at the section.
- How many degrees are in a right angle?
- Which instrument measures an angle in degrees?
Check the warm-up
- .
- A protractor.
If an answer differs, revisit Section 16.1 for right angles and measuring angles.
Try these with help
1. Construct the perpendicular bisector of a 6 cm segment.
Hint
Keep the compass wider than half the segment.
Next step
Draw equal arcs from both endpoints, then join their crossings.
Full answer
The line through the two arc intersections is the perpendicular bisector.
2. Bisect an angle of using compasses.
Hint
Use equal arcs from the two points where an arc meets the arms.
Next step
Join the angle vertex to the crossing of the equal arcs.
Full answer
The bisector divides the angle into two angles of .