呃...的确是一元二次方程...(X-30)*[600-(X-40)*10]=10000(X-30)*(600-10X+400)=10000(X-30)*(1000-10X)=100001000X-10X^2-30000+300X=1000010X^2-1300X+40000=0X^2-130X+4000=0(X-80)(X-50)=0得：X1=80,X2=50...