M3.6.4 For the adult
Area of triangles and parallelograms
A leaning shape has the same base and height as a rectangle. Does it hold less space?
What this chapter teaches
A parallelogram has the same area as a rectangle with the same base and height, because one cut triangle can slide to the other end. A triangle is half of a parallelogram. The height is always measured at a right angle to the base, never along a slanted side.
Three questions to ask
There is no one right wording. Listen for the idea.
- How can you turn a parallelogram into a rectangle with one cut?
- Why do we halve base × height for a triangle?
- A parallelogram has sides of 8 cm and 5 cm, and a height of 4 cm. Which numbers do you multiply?
After the chapter, the learner can
- Find the area of a parallelogram as base × height
- Find the area of a triangle as half of base × height
What they copy into their notebook
Height is at a right angle to the base, never the slanted side. Parallelogram: base × height. Triangle: half of base × height.