Indestructible Perpendicular Lines
Indestructible perpendicular lines are constructed using two circles. First draw one circle, and then a second, whose center lies outside of the first circle. Draw a line connecting the centers of the two circles. Then draw a line connecting the points of intersection of the circles. These two lines are perpendicular. No matter how big or small you now make the circles or rotate the circles, those two lines are indestructibly perpendicular.