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Year 8 - Maths

Bisecting an angle

Constructions

Unit Summary

In this unit we develop skills in using a pair of compasses and ruler to construct various accurate shapes and angles including triangles, rhombi, perpendicular lines and angle bisectors.

Lesson Summary

You will learn to use the properties of a rhombus to construct an angle bisector.

Key Notes

  • A rhombus can be constructed from two congruent isosceles triangles.
  • The diagonals of a rhombus bisect the angles.
  • It is possible to construct an angle bisector without drawing the rhombus.

Vocabulary To Learn

  • Bisect: To bisect means to cut or divide an object into two equal parts.
  • Rhombus: A rhombus is a parallelogram where all sides are the same length.
  • Congruent: If one shape can fit exactly on top of another using rotation, reflection or translation, then the shapes are congruent.

Common Mistakes To Avoid

  • I can use a protractor to measure an angle, then half that angle to bisect it.

3 Quick Questions (With Answers)

1. Solve this in steps: explain the method from this lesson and why each step matters.

A rhombus can be constructed from two congruent isosceles triangles. The diagonals of a rhombus bisect the angles.

2. Use this key word in a maths sentence and explain it clearly. 'Bisect'

To bisect means to cut or divide an object into two equal parts. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: I can use a protractor to measure an angle, then half that angle to bisect it. Correction: Constructions, such as bisecting an angle, are methods of creating & modifying shapes & angles in ways that don't require measurement tools.

More Lessons In This Unit

Browse all guides in the Year 8 Maths guide library.