試解

來源: 於 2026-03-20 16:52:27 [舊帖] [給我悄悄話] 本文已被閱讀：次

Extend DE to F. Obviously, ABFD=21*2=42, which means ADC=21, which means ADE=21-12=9, which means BFE=21-9=12.

Let EFC area =x. Observe that BFE and EFC share the same bottom line, while EFC and ADE are similar. So, 12/x= BF/FC=AE/EC= sqrt(9/x)

x=144/9=16

Whole area = 42+12+x=70