9/(9+x)-4/(4+x)=0.1
问题描述：
9/(9+x)-4/(4+x)=0.1
答
原式=（36+9x-36-4x）/（9+x）（4+x）=0.1
5x/（36+13x+x^2）=0.1
0.1x^2+1.3x+3.6=5x
x^2+13x+36-50x=0
x^2-37x+36=0
（x-1）（x-36）=0
x=1或x=36
答
两边乘10(x+9)(x+4)
90x+360-40x-360=x²+13x+36
x²-37x+36=0
(x-1)(x-36)=0
x=1,x=36
经检验,x=1和36是方程的解