abc4567
幼苗
共回答了20个问题采纳率:95% 举报
1/2*(100+180)x+2(80-x)x=1/6*1/2*(100+180)*80
(50+90)x+2(80-x)x=1/3*(50+90)*40
140x+2(80-x)x=1/3*140*40
140x+160x-2x^2=1/3*140*40
70x+80x-x^2=1/3*140*20
210x+240x-3x^2=2800
450x-3x^2=2800
3x^2-450+2800=0
x^2-150x+2800/3=0
x^2-150x+5600-5600+2800/3=0
(x-75)^2-16800/3=0
(x-75)^2-50400/9=0
(x-75-60√14)(x-75+60√14)=0
x=75+60√14或x=75-60√14
1年前
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