1.(10+x)(500-20x)=6000
2.10(x-3)+x=x²
3.1600(1+x)²-1600=1936
4.(x-1)²+x²=(x+1)²
5.(2.+2x)(40-x)=1200
(10+x)(500-20x)=6000
5000+500x-200x-20x^2=6000
20x^2-300x+1000=0
x^2-15x+50=0
(x-5)*(x-10)=0
x=5,x=10
2.10(x-3)+x=x²
10x-30+x=x^2
x^2-11x+30=0
(x-5)(x-6)=0
x=5,x=6
3.1600(1+x)²-1600=1936
1600(1+2x+x^2-1)=1936
2x+x^2=1.21
x^2+2x-1.21=0
x=-1±根号2.21
4.(x-1)²+x²=(x+1)²
x^2=(x+1)²-(x-1)²
x^2=(x+1+x-1)(x+1-x+1)
x^2=4x
x=0,x=2
5.(2+2x)(40-x)=1200
(1+x)(40-x)=600
40+40x-x-x^2=600
x^2-39x+540=0
△=39^2-540*4<0
无解
追问第四道算错了吧?额,第五道题是(20+2x)(40-x)=1200
追答第四
x=0,x=4
(20+2x)(40-x)=1200
(10+x)(40-x)=600
400+40x-10x-x^2=600
x^2-30x+200=0
也是无解
第五道有解,(-30)²-4X200=100>0的啊
追答x^2-30x+200=0
(x-10)(x-20)=0
x=10,x=20
实在抱歉,我看错数了
http://zhidao.baidu.com/question/1830271072662190020.html?quesup2&oldq=1 谢了