Boyd/Usilton

1. If an animal is a robin, then the animal is a bird.

2. If an angle measures 130, then the angle is obtuse.

3. Vertical angles have a vertex.

4. Dolphins are mammals.

1. If a woman is born in Florida, then she is American.

2. If a number is divisible by 3, then it is odd.

3. If a month has 28 days, then it is February.

4. If two angles form a linear pair, then they are supplementary.

1. A leap year is a year that has 366 days because one day is added to the month of February.

2. A light bulb gives off light and is hot to the touch.

3. Opposite rays are two rays that share the same endpoint.

4. Linear pairs of angles are two adjacent angles that share one side, and the sides they do not share are opposite rays.

If the converse is true and the statement can be written as a biconditional the definition is a good definition.

If the converse is false or you can find a counterexample, the defintion is not a good definition.