x^2-y^2=72; x^2-(-x+9)^2=72 x=8.5
x+y=9 y=-x+9 y=0.5
1) x^2-(-x+9)^2=72
x^2-(x^2-18x+81)=72
x^2-x^2+18x-81-72=0
18x-153=0
18x=153
x=8.5
x^2-y^2=72; x^2-(-x+9)^2=72 x=8.5
x+y=9 y=-x+9 y=0.5
1) x^2-(-x+9)^2=72
x^2-(x^2-18x+81)=72
x^2-x^2+18x-81-72=0
18x-153=0
18x=153
x=8.5