x+y=100 xy=2400 x=100-y (100-y)y=2400 100y-y^2-2400=0 y^2-100y+2400=0 D=10000-4*2400=400 y1=(100+20)/2=60 y2=80/2=40 y1=60 x1=40 y2=40 x2=60