(1200-50X)(30+X)=28000

问题描述:

(1200-50X)(30+X)=28000

(1200-50X)(30+X)=28000
36000-1500X+1200X-50X^2=28000
50X^2+300X=8000
X^2+6X-160=0
(X+16)(X-10)=0
X=-16,X=10.