Suppose you are given a piece of tracing paper with a circle on it and you do not have a compass. How can you use paper folding to inscribe a square in the circle?
Fold the circle so that one half coincides with the other. The crease is a radius of the circle. Then
fold this crease onto itself to make a second crease that is the perpendicular trisector of the first.
These two creases intersect the circle at the vertices
of an inscribed square.

answer: the proof is mentioned below.

step-by-step explanation:

since, given:   lines bc = ef

prove:   lines ac > ef

          statements                                           reason

1. bc=ef                                           1. given

2. ac= ab+bc                                 2. because b is the point between the  

                                                            line segment ac

3.   ac > bc                                       3. because if a line segment is equal to

                                                          the sum of two line segments then it is

                                                          always greater then each of these

                                                          individual line segments

4. ac > ef                                         4. by equality property.