Area ratios
From AoPSWiki
If two triangles share a height, then the ratio of their areas is equal to the ratio of their bases. If two triangles share a base, then the ratio of their areas is equal to the ratio of their heights.
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If two triangles share a height, then the ratio of their areas is equal to the ratio of their bases. If two triangles share a base, then the ratio of their areas is equal to the ratio of their heights.

