Ta có: x.y = 2.5 = 10
x^2 + y^2 = 5^2 = 25 
=> (x + y)^2 - 2xy = 25
<=> (x + y)^2 - 2.10 = 25 => (x + y)^2 = 45 => x + y = 3√5 => x = 3√5 - y
Do đó: (3√5 - y)y = 10
<=> y^2 - 3√5y + 10 = 0
<=> y = 2√5 hoặc y = √5
y = 2√5 => x = √5
y = √5 =>x  = 2√5