When a straight line set up on a straight line makes the adjacent angles equal to one another, each of the equal angles is right, and the straight line standing on the other is called a perpendicular to that on which it stands.
— Euclid Ancient

Father of geometry

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Details

Context

Definition in 'Elements'

Date / Period

300 BC

Category

Strange & Unusual

Source

https://mathcs.clarku.edu/~djoyce/java/elements/bookI/defI10.html

Verification

Confirmed

Explanation

Found in 2 providers: deepseek,grok

Method

Cross Reference

Sources Checked

2 sources

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