Question

If an angle measures 90°, then it is a right angle.

Which of the following arguments is valid with respect to the conditional statement premise above?

1. An angle does not measure 90°.
Therefore, it is not a right angle.
2. An angle measures 90°.
Therefore, it is a right angle.
3. An angle is a right angle.
Therefore, it measures 90°.
4. An angle is not a right angle.
Therefore, it does not measure 90°.

A. 2 only
B. 1 and 3
C. 2 and 4
D. All arguments are valid.

Answer 1

The answer based on the original statement is A: 2 only.

Explanation:

It might seem obvious to be D, becasue we both know that all of the statements are true. But, based on the statement, we don’t necessarily know that. The statement only tells us that if a angle is 90 degrees it is a right angle. It does not specify if another angle such as 91 degrees would also be considered a right angle. Therefore, we would not be able to draw any other conclusions other than number 2 based on the statement given in the question.