(8/7x)+x=600
(8＋7x^2)/7x=600
8＋7x^2=4200x
7x^2-4200x+8=0
x^2-600x+8/7=0
x^2-600x+300^2=300^2-8/7
(x-300)^2=89998*6/7
x-300=±（2√944979）/7
x1=300+（2√944979）/7
x2=300-（2√944979）/7