M4.3.1 For the adult
Pythagoras' theorem
A triangle has a right angle and two short sides of 3 cm and 4 cm. How long is the third side?
What this chapter teaches
In a right angled triangle the squares on the two shorter sides add up to the square on the longest side. The chapter shows why with a cut and move picture, then uses the rule to find a hypotenuse or a leg, and to test whether three sides make a right angle.
Three questions to ask
There is no one right wording. Listen for the idea.
- Which side is the hypotenuse, and how can you tell without measuring?
- Why do you add the squares to find the hypotenuse but subtract them to find a leg?
- How could you use a piece of string with 12 equal spaces to make a square corner?
After the chapter, the learner can
- Find the longest side of a right angled triangle
- Find a shorter side when you know the other two
- Show that sides 5, 12 and 13 make a right angle
What they copy into their notebook
In a right angled triangle, a² + b² = c². The hypotenuse c faces the right angle. Add squares to find c. Subtract squares to find a leg.