{x^2+y^2=26 => (x+y)^2-2xy=26 {xy-5=0 {(x+y)^2-2xy=26 {xy=5 {(x+y)^2-10=26 {xy=5 { (x+y)^2=36 {xy=5 {x+y=6 {xy=5 {y=6-x {6x-x^2=5 {x^2-6x+5=0 D=36-4*1*5=V16 =4 x=6+4/2=5 x2=6-4/2=1 y=1 y=5