Area - Trapeziums
The area of any trapezium is the same as a suitable rectangle divided by two.
First we draw a second inverted trapezium to create a parallelogram.
We then draw a rectangle the same length as the parallelogram.
This rectangle is the same length as the top plus the bottom of the trapezia.
We can see that the small red triangle on the left will exactly fit over
the blue triangle on the right.
Obviously the area of the parallelogram is equal to the area of the rectangle.
So the area of one trapezium is half the area of the rectangle.
To work out the area of a trapezium we use a simple formula:
area = (top + bottom) x perpendicular height ÷ 2
Notice that the height is the perpendicular [at right angles]
distance from the base to the top and not one of the sides.
So for this trapezium:
area = (3 + 8) x 4 ÷ 2 = 22 cm²
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