作者mack (脑海里依然记得你)
看板CS_TEACHER
标题Re: [请益] 请问一题资优数学
时间Tue Feb 19 05:37:06 2013
假设△DEF=3x
=> DE:AB = 3x:(9+15) = 3x:24 = x:8
=> △DEF:△ABC = DE^2:AB^2 = x^2:64 = 32:(32+3x+9+15) = 32:(3x+56)
=> 3x^3+56x^2 = 32*64
=> 3x^3+56x^2-32*64 = 0
=> (3x-16)(x^2+24x+128)=0
=> △DEF = 3x = 16
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