※ 引述《jenshi (小旭)》之銘言：
: https://imgur.com/a/Cx1DBM7
: 求CF
給推文以外的方式
△ABD ~ △EBA => AF = 20/3
BE = 50/3
AB中點K => KF = 25/3
△CFK ~ △CBD => (BC + 5) : 25/3 = CD : 8
=> 8BC + 40 = CD 25/3 -------(1)
△KCD ~ △FCA => CD : 5 = (10 + BC) : 20/3
=> CD 20/3 = 50 + 5BC -------(2)
=> CD = 120/7
=> FC = 120/7 + 20/3 = 500/21
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