1. Recap: What’s the area?

2. Recap: What’s the area?

3. Half of a rectangle…
What’s the area?

4. Half of a rectangle…
What’s the area?

5. This triangle can be split into two rectangles.
What’s the area?

6. This triangle can also be split into two rectangles…
This triangle can also be split into two rectangles…. Can you see why it is still half of the surrounding rectangle?
What’s the area?

7. These triangles have the same area.
How do we know?
They both have the same base and height, so they are both half of the same rectangle.

8. 4 Questions
Calculate the area of each of these triangles. Deduce a quick way/formula for finding the area.

9. Does ½ × base × height still work?
Part 2: Overhanging Triangles
Why is this an overhanging rectangle? Why does the formula/method still work? What is the height of this triangle?
Does ½ × base × height still work?

10. YES! Overhanging Triangles
Calculate the are of the pink right angled triangles and subtract them from the rectangle – the area is still half base x height.
YES!

11. Why? Overhanging Triangles
All triangles are half of a parallelogram. What is the area of this parallelogram?
Why?

12. Why? Overhanging Triangles
We can cut off the end of the parallelogram and it will fit exactly on the other side… so what is the area of the paralleogram? Base x height of the triangle.
Why?

13. 4 Questions
Calculate the area of these overhanging triangles.

14. What would you need to measure in order to work out the area of this triangle?
Discuss meaning of perpendicular height.

15. This slide is provided to convince any students who aren’t sure about which lengths should be measured.

16. End of Lesson
Draw a triangle in your book. Measure its area.
Swap with a partner and see if they agree with your measurements and calculations.