[justify]Try to figure out how the number b depends on the number a. To do this, move the point a over the real line (click and drag the small blue ball) and try to identify what happens with the point b! To check your answer, write in the text field below an algebraic expression in terms of a and, then, click on the button “Am I right?”. It is important that your answer matches with the point b for all positions of the point a! You can click on the icon in the lower right corner (shaped like a square within a circle) to maximize the screen.[/justify]

Tutorial (looping video as an animated GIF):