Here is an equilateral triangle with sides of length 1.
Let's define a unit of area, $T$, such that the triangle has area $1T$.
Here are some parallelograms whose side lengths are whole numbers.
Can you find the area, in terms of $T$, of each parallelogram?
Compare the results with the lengths of their edges.
What do you notice?
Can you explain what you've noticed?
Can you find a similar result for trapeziums in which all four lengths are whole numbers?
You might like to try More Isometric Areas next.