This is a geometrical presentation of the formula
The difference between the areas of the [b][i]a[/i][/b]-sided and the [b][i]b[/i][/b]-sided squares equals the area of the rectangle whose sides are [b][i]a+b[/i][/b] and [b][i]a-b[/i][/b].
The sliders allow to check it as [b][i]a[/i][/b] and [b][i]b[/i][/b] change
Then there are some exercises to apply the formula
