(60-x)(120-x)=800

问题描述:

(60-x)(120-x)=800
x是多少

7200-120x-60x-x2-800=0
x2+180x-6400=0
(x+90)2=6400+8100
(X+90)2=14500
x=120.42-90=30.42
或者x=-120.42-90=-220.42