2分之1(100+180)x+2(80-x)x=6分之1乘2分之1（100+180）乘80怎么算?我好蠢不晓得算...帮哈我撒.我就要明天要交作业.

Question

2分之1(100+180)x+2(80-x)x=6分之1乘2分之1（100+180）乘80 怎么算?我好蠢不晓得算...帮哈我撒.
我就要 明天要交作业.

Answer 1

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