In Mathematics, what is the difference between one stroke and double strokes in shapes and solids?

In Mathematics, about shapes and solids, if you see some diagrams you'll see the line/stroke marked on shapes telling that both lengths are equal. For example, in an equilateral triangle, all three sides marked with 1 stroke each a href="http://upload.wikimedia.org/wikipedia/commons/thumb/9/96/Triangle.Equilateral.svg/220px-Triangle.Equilateral.svg.png" rel="nofollow"http://upload.wikimedia.org/wikipedia/co…/a However, I see some uses only 1 stroke and some double. What do they mean? I hope to receive your answer b4 i ask my math teacher