As shown in the figure, ad is the middle line of △ ABC, point E is on the extension line of BC, CE = AB, ∠ BAC = ∠ BCA, verification: AE = 2ad

As shown in the figure, ad is the middle line of △ ABC, point E is on the extension line of BC, CE = AB, ∠ BAC = ∠ BCA, verification: AE = 2ad

To extend ad to m, make DM = ad, and adthe midline of △ ABC, DB = CD, DB = CD, in △ abd and △ MDC, BD = CD, in △ abd and △ abd △ MCD (SAS), DM = ad, so that DM = ad, ad is the midline of △ ABC, DB = CD, in △ abd and △ MDC, in △ abd and △ MDC, in △ abd and △ abd and △ MDC, BD = CD = CD = CD Δace (SAS) ).∴AE=AM,∵AM=2AD,∴AE=2AD.