[TEX]\blue t=x+\sqrt{x^2+1}\righ dt=\(1+\frac{x}{\sqrt{x^2+1}}\)dx=\(\frac{x+\sqrt{x^2+1}}{\sqrt{x^2+1}}\)dx[/TEX]
[TEX]\red \righ I=\int_{t=x+\sqrt{x^2+1}} tdt= \frac{1}{2}t^2+C[/TEX]
[TEX] \blue\righ I=\frac{1}{2}\( x+\sqrt{x^2+1}\)^2+C[/TEX]
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