Students` Learning Outcomes

  • Use compasses and straightedge/ruler to construct equilateral, isosceles and scalene triangles when three sides are given.
  • Use protractor and straightedge ruler to construct equilateral, isosceles and scalene triangles when two angles and included side are given. Measure the length of remaining two sides and one angle of the triangle.

Information for Teachers

  • Construct triangles when three sides are given e.g. 8 cm, 7 cm, and 6 cm
  • Step 1: Draw a line 8 cm long
  • Step 2: Open compasses up to 7 cm. put your compass point on A and make an arc above the line.
  • Step 3: Open compasses up to 6 cm. put the compass sharp side on B and make an arc to cut the arc you drew in step in step 3. Where the arcs meet is point C.
  • Step 4: Connect point C to points A and B


  • This is a scalene triangle. Same method will be used to draw rest of the two triangles. Use ruler and draw a base line of given length.
  • Consult text book while teaching lessons wherever required.


Material / Resources

Writing board, chalk / marker, duster, geometry box, textbook


  • Revise information related to the characteristics of triangles with students according to the given instructions to draw triangles.


  • Brainstorm with the class about “The properties of triangles”.



  • Facts you should get include; three sides, three angles / corners, angles add to 1800. Different types (Scalene / isosceles / equilateral / right –angled)
  • Beware of students saying that triangles have all sides the same length or all angles the same.
  • Ask students how they could construct an equilateral triangle.



  •  Discuss their ideas-using compass (when angles are given). Then tell them that today we are going to look at the method of using compass as with protractor we have already done in last lesson.



Activity 1

  • Prepare students to get ready for work in groups.
  • Ask them to take out their notebooks and geometry boxes.
  • Write question on the board that we are going to construct a scalene triangle with following measurements 8 cm, 6 cm, and 7 cm.


  • Give them some time to try, by using a compass and ruler.
  • Then you say each of the steps in key points and ask them to perform.
  • Some of them will be able to follow.
  • Then demonstrate these steps on the board by doing it yourself.
  • Now ask the students to attempt the same question individually.
  • Give few more questions to the students.
  • Invite two or more students one by one to recap the method with the class.


Activity 2

  • Write down a question on the board. (Construct a triangle ABC with one side of 7 cm and included angles of 450 and 600)


  • The constructed triangle ABC will be acute angle triangle.


Sum up / Conclusion

  • Revise new learning with the students.

o   A triangle has three sides or edges and three angles.

o   A triangle is considered as one of the basic closed shapes of geometry.

o   Triangles can be classified according to sides and angles

o   Triangles on the basis of angles: Acute-Angled Triangle, Right-Angled Triangle, Obtuse-Angled Triangle

o   Triangles on the basis of Sides: Scalene Triangle, Isosceles Triangle, Equilateral triangle


  • Consult textbook while teaching the lessons wherever required.


  • Ask the students to write process how to draw different types of triangles so you can assess them. E.g. Acute –Angled, Right-Angled, Obtuse-Angled, Scalene, Isosceles, Equilateral
  • Involve the students in solving the problems given at the end of the lesson of textbook

Follow up

  • Encourage students to draw triangles using different measurements.
  • Assign two questions to students for home-work; try to give different questions to different groups. This will increase their interest towards home assignments.



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