Решить систему уравнений { x^2- у^2= 72 { x+у=9

x^2-y^2=72 x+y=9 y = 9-x x^2-(9-x)^2 = 72 x^2 - (81-18x+x^2) = 72 x^2 -81 +18x -x^2 = 72 18x = 153 x = 153/18 = 17/2 = 8.5 (17/2)^2 - y^2 = 72 289/4-72 = y^2 1/4 = y^2 1/2 = y --- y=  1/2, x = 17/2

Я ни разу не решал систему уравнений, не обессудьте. [latex] \left \{ {{x^2-y^2=72} \atop {x+y=9}} \right. [/latex] [latex]x=9-y[/latex] [latex](9-y)(9-y)-y^2=72[/latex] [latex]81-18y+y^2-y^2=72[/latex] [latex]81-18y=72[/latex] [latex]-18y=-81+72[/latex] [latex]-18y=-9[/latex] [latex]y=0.5[/latex] [latex]x=9-0.5[/latex] [latex]x=8.5[/latex]