Mathematics

Mathematics

Problem

In △ABC\triangle ABC, point DD is the midpoint of ABAB. A line through DD parallel to BCBC meets ACAC at EE. Prove that EE is the midpoint of ACAC.
Intuitive explanation

This is the midpoint theorem in action—a beautiful consequence of similar triangles and proportional sides. Since DE∥BCDE \parallel BC, triangles ADEADE and ABCABC are similar, which means their corresponding sides are proportional. The key insight is that because DD divides ABAB in the ratio 1:11:1 (it's the midpoint), the same ratio must hold for how EE divides ACAC. Use the proportionality of similar triangles to show that AE=ECAE = EC.

Intuitive explanation

This is the midpoint theorem in action—a beautiful consequence of similar triangles and proportional sides. Since DE∥BCDE \parallel BC, triangles ADEADE and ABCABC are similar, which means their corresponding sides are proportional. The key insight is that because DD divides ABAB in the ratio 1:11:1 (it's the midpoint), the same ratio must hold for how EE divides ACAC. Use the proportionality of similar triangles to show that AE=ECAE = EC.

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