Omar Khayyam · Mathematics

What Is a Number? Ratios and the Reality of the Irrational

In the second part of his Euclid commentary, Khayyam reexamined the theory of ratios in Book V of the <em>Elements</em> and pressed a revolutionary idea: that a ratio - even between incommensurable magnitudes - is itself a kind of number. In treating irrational magnitudes as numbers, he took an early step on the road to the real numbers.

What you'll be able to recall

You learned that Khayyam scrutinized Euclid&rsquo;s Book V theory of proportion, connected it to an older definition based on the process now linked to continued fractions, and argued that ratios of magnitudes - including incommensurable ones - are genuine numbers. Explain why treating irrational ratios as numbers was…

Leads to Euclid.

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