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Concept

Counterexample

A counterexample is an example that shows a conjecture is false. For example, consider a conjecture stating that all shapes with four congruent sides are squares. A counterexample for this conjecture is a rhombus.
Conjecture and its counterexample
Although a rhombus has four congruent sides, it is not a square because its angles are not right angles. Therefore, rhombuses are examples that disprove the conjecture.
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