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1. I=[tex]\int_{-1}^{1}[/tex][tex]\frac{dx}{x+1+\sqrt{x^2+1}}[/tex]
2. [tex]\left\{ \begin{array}{l} x^2+y^2+\frac{2xy}{x+y} = 1 \\ \sqrt{x+y}=x^2-y \end{array} \right.[/tex]
2. [tex]\left\{ \begin{array}{l} x^2+y^2+\frac{2xy}{x+y} = 1 \\ \sqrt{x+y}=x^2-y \end{array} \right.[/tex]