Constructing Triangles with Compasses and Protractors

Differentiated Learning Objectives

• All students should be able to construct a triangle using SSS.
• Most students should be able to construct a triangle using SSS and SAS,
• Some students should be able to construct a triangle using SSS, SAS and ASA.

Links to Lesson Resources (Members Only)

Starter/Introduction

The start of the lesson encourages students to work in pairs and discuss the symmetrical properties of a square. Encourage students to use mathematical keywords such as symmetry, reflection, square, rectangle, and triangle.

 Prompts / Questions to consider

• What is reflective symmetry?
• Which shape could be half a right-angled triangled triangle?

Constructing Triangles with Compasses and Protractors

Click here to view the video.

The key points when constructing triangles with compasses and protractors are:

Equipment Needed

Side, Angle, Side: Pair of compasses, rule and protractor

Angle, Side, Angle: Ruler and pair of compasses

Side, Side, Side: Pair of compasses and ruler

Right-angle, Hypotenuse, Side: Pair of compasses and ruler

Students need to observe their teacher using the same equipment they will use. If possible, the teacher should use a visualiser to work at their desk with the same equipment.

Encourage students to work to an accuracy of 2 mm and 2 degrees. Encourage students to work in pairs so they can check the accuracy of their peer’s work.

 Prompts / Questions to consider

• What type of triangle is it? (SAS, ASA, SSS, RHS)
• What equipment is needed?
• Which scale do I use on the protractor?

Plenary

The plenary challenges students to connect their understanding of the properties of quadrilaterals to constructions. This activity takes between 10 to 12 minutes.

 Prompts / Questions to consider

• How can I use the formula to work out the calculation?
• Can I use a pair of brackets to make the calculation simpler?
• How can I use the fraction and mixed number button on a calculator to check my solution?

Differentiation

Some students struggle with the dexterity of using a pair of compasses to a suitable degree of accuracy. Encourage students to rotate the paper/book rather than the compasses. Less able often use the incorrect scale on a 180° protraction. To support this, remind students about the difference between acute and obtuse angles.

Additional Resources

 

Fractions

Problem solving lesson on fractions. There are five problems that link to ratio, probability and averages.

 

Adding and Subtracting Fractions with the same Denominator Revision Lesson

Revision lesson on adding and subtracting fractions for exam students.

Ages 11 - 13

Calculations with Fractions and Mixed Numbers

Students solve a wide range of problems with fractions and mixed numbers.