M3.5.3 For the adult
Triangles
Do the three angles of every triangle add up to the same number?
What this chapter teaches
The three angles of any triangle add to 180°, because the corners fit side by side along a straight line. This gives a missing angle. The names equilateral, isosceles, scalene and right angled say what kind of triangle it is.
Three questions to ask
There is no one right wording. Listen for the idea.
- Two angles of a triangle are 50° and 60°. What is the third, and how did you work it out?
- Why are the two base angles of an isosceles triangle equal?
- Can a triangle have two right angles? Why not?
After the chapter, the learner can
- Show that the angles of a triangle add up to 180°
- Find a missing angle in a triangle
- Name equilateral, isosceles, scalene and right angled triangles
What they copy into their notebook
The three angles of a triangle add to 180°. Equilateral: 3 equal sides, all angles 60°. Isosceles: 2 equal sides, 2 equal angles. Scalene: none equal. Right angled: one 90° angle.