x-30)[600-(x-40)×10]=10000,10(x-30)(100-x)=10000,两边除以10得(x-30)(100-x)=1000,多项式的乘法100x-x^2-3000+30x=1000,-x^2+130x-3000=1000x^2-130x+4000=0(x-50)(x-80)=0x1=50,x2=80