Which biconditional is not a good definition? a whole number is odd if and only if the number is not divisible by 2. an angle is straight if and only if its measure is 180°. a whole number is even if and only if it is divisible by 2. a ray is a bisector of an angle if and only if it splits the angle into two angles.

The correct answer is:

A ray is a bisector of an angle if and only if it splits the angle into two angles.

Explanation:

To "bisect" means to split into two congruent pieces.  The statement we are given is that the ray splits the angle into two angles, not that it splits it into two congruent angles.  Thus this is not a good definition.

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.