PRINCIPIA · THEOREM

Right triangle — the median to the hypotenuse equals half the hypotenuse

Dependencies: Parallelogram tests (F.04), Rectangle tests (F.07), Rectangle: equal diagonals (F.06).

Statement

Let △ABC\triangle ABC have ∠C=90∘\angle C = 90^\circ, and let MM be the midpoint of the hypotenuse ABAB. Then the median to the hypotenuse has length exactly half the hypotenuse, and MM is equidistant from the three vertices:

∣CM∣  =  ∣AM∣  =  ∣MB∣  =  12 ∣AB∣.|CM| \;=\; |AM| \;=\; |MB| \;=\; \tfrac{1}{2}\,|AB|.

In other words, the midpoint of the hypotenuse of a right triangle is equidistant from the three vertices — another way of stating that it is the centre of the circumscribed circle, with the hypotenuse as the diameter.

Right \triangle ABC with the median CM to hypotenuse AB; the three segments CM, AM, MB are all equal.

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