Proof by contradiction is a powerful tool.
Father of geometry
While Euclid extensively used proof by contradiction (reductio ad absurdum) throughout 'Elements', this specific phrasing is a modern summary of his method, not a direct quote.
c. 300 BCE (implied by method)
Found in 1 providers: grok
Cross Reference
1 source
"A circle is a plane figure contained by one line such that all the straight lines falling upon it from one point among those lying within the figure are equal to one another."
Strange & Unusual"Things which are equal to the same thing are also equal to one another."
Strange & Unusual"A line is breadthless length."
Strange & Unusual"To cut off from the greater of two given unequal straight lines a straight line equal to the less."
Strange & Unusual"To produce a finite straight line continuously in a straight line."
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