Given some line segment AB, whose length you do not know, construct such that the length of is twice that of .

Steps of Construction-

1. Draw a line segment AB.

2. Keep the needle of compass on A and other end of it on B.

3. Draw point P. Put the needle of compass on P and draw an arc, naming it as R. Again draw an arc by putting the needle on R such that PR extends to Q.

4. Hence, PQ is the twice of AB.