Toán Lớp 9: cho `x, y` thỏa mãn `x+sqrt{y^2+1}.y+sqrt{x^2+1}=0`. cm `x+y=0` -

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Toán Lớp 9: cho `x, y` thỏa mãn `x+\sqrt{y^2+1}.y+\sqrt{x^2+1}=0`. cm `x+y=0`