# Definition:Triangle (Geometry)/Scalene

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## Definition

A **scalene triangle** is a triangle in which all three sides are of different lengths.

## Euclid's Definition

In the words of Euclid:

*Of trilateral figures, an***equilateral triangle**is that which has its three sides equal, an**isosceles triangle**that which has two of its sides alone equal, and a**scalene triangle**that which has its three sides unequal.

(*The Elements*: Book $\text{I}$: Definition $20$)

## Sources

- 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**scalene triangle**