Question

Cho \(\left(x+\sqrt{x^2+2010}\right)\left(y+\sqrt{y^2+2010}\right)=2010\)

Tính S=x+y

Answer 1

theo đề bài \(\left(x+\sqrt{x^2+2010}\right)\left(y+\sqrt{y^2+2010}\right)=2010\)

mà \(\left(\sqrt{x^2+2010}+x\right)\left(\sqrt{x^2+2010}-x\right)=2010\)

nên \(\sqrt{x^2+2010}-x=\sqrt{y^2+2010}+y\)

hay \(x+y=\sqrt{x^2+2010}-\sqrt{y^2+2010}\) (1)

Tương tự \(\left(\sqrt{y^2+2010}+y\right)\left(\sqrt{y^2+2010}-y\right)=2010\)

nên \(\sqrt{x^2+2010}+x=\sqrt{y^2+2010}-y\)

hay \(x+y=\sqrt{y^2+2010}-\sqrt{x^2+2010}\) (2)

Từ (1) và (2) suy ra S = x + y = 0.