Ivan Shishkin, Rye (1878)

Problems/GeometryReviewed

Equality of areas in a triangle

by goldfinch·translated by Ancient Tree·
5
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Show that the areas of the two triangles ABMABM and ACMACM, defined by a median of an arbitrary triangle ABCABC as in the following figure, are equal.

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Solution by Ancient Tree

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Image2
By definition, the median of ABCABC from vertex AA splits BCBC into two segments of same length :
BM=MCBM=MCFurthermore, the two triangles ABMABM and AMCAMC have the same height AHAH.

The area of the two triangles are respectively BM×HA2\frac{BM \times HA}{2} and MC×AH2\frac{MC\times AH}{2}, which are therefore equal.

Solution by goldfinchFR

Discussions0 useful votes

Image2
Par définition, la médiane du triangle ABCABC issue du sommet AA coupe BCBC en deux segments de même longueur :
BM=MCBM=MCPar ailleurs, les deux triangles ABMABM et AMCAMC ont la même hauteur AHAH.

Les surfaces des deux triangles qui valent respectivement BM×HA2\frac{BM \times HA}{2} et MC×AH2\frac{MC\times AH}{2} sont donc identiques.

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