Final answer:
The conditional 'If a polygon is an octagon, it has eight sides' is true by definition, as an octagon is a polygon with exactly eight sides. No counterexample is needed since the statement is accurate.
Step-by-step explanation:
The student has asked to determine if the following conditional is true or false: 'If a polygon is an octagon, it has eight sides.' This statement can be evaluated for its truth by understanding the definitions involved. A polygon is a closed figure with straight sides, and an octagon is specifically defined as a polygon with eight sides. Therefore, the necessary and sufficient condition for a polygon to be categorized as an octagon is indeed that it has eight sides.
Since an octagon by definition has eight sides, the conditional given is true. There is no need for a counterexample in this case, as a counterexample is used to disprove a statement, and this statement is factually correct based on the definition of an octagon.