1)（x-30)*[600-10(x-40)]=10000
600x-18000-10*(x-30)(x-40)=10000
600x-10(x^2-70x+1200)=10000+18000
10x^2-700x+12000+28000-600x=0
x^2-130x+4000=0
(x-65)^2=225
x=80 x=50
2) （500－10x)[(50+x)-40]=8000
(50-x)*[(50+x)-40]=800
2500-x^2-(2000-40x)=800
x^2-40x+300=0
(x-20)^2=100
x=10 x=30
好累啊,好久没算了,