A right-angled triangle is like half a rectangle. So to calculate the area of a triangle, you can work out the area of the rectangle and then divide by 2. The formula for working out the area of a ...

You can see that the area of the right-angled triangle is half the area of the rectangle. So you could divide the area of the rectangle you calculated above by 2. 40cm² ÷ 2 = 20cm² ...