Question
Evaluate the definite integral $\int_{0}^{1} \frac{d x}{\sqrt{1+x}-\sqrt{x}}$

Answer

Integral to be evaluated: $\int_{0}^{1} \frac{d x}{\sqrt{1+x}-\sqrt{x}}$ 
Let $I=\int_{0}^{1} \frac{d x}{\sqrt{1+x}-\sqrt{x}}$ 
= $\int_{0}^{1} \frac{1}{\sqrt{1+x}-\sqrt{x}} \times \frac{\sqrt{1+x}+\sqrt{x}}{\sqrt{1+x}+\sqrt{x}} d x$ 
= $\int_{0}^{1} \frac{\sqrt{1+x}+\sqrt{x}}{1+x-x} d x$ 
= $\int_{0}^{1} \frac{\sqrt{1+x}+\sqrt{x}}{1} d x$ 
= $\int_{0}^{1} \sqrt{1+x} d x+\int_{0}^{1} \sqrt{x} d x$ 
= $\int_{0}^{1}\left((1+x)^{\frac{1}{2}}\right) d x+\int_{0}^{1}(x)^{\frac{1}{2}} d x$ 
$\Rightarrow \mathrm{I}=\left[\frac{(1+\mathrm{x})^{\frac{3}{2}}}{\frac{3}{2}}\right]_{0}^{1}+\left[\frac{(\mathrm{x})^{\frac{3}{2}}}{\frac{3}{2}}\right]_{0}^{1}$ 
= $\frac{2}{3} \cdot\left[(1+1)^{\frac{3}{2}}-(1+0)^{\frac{3}{2}}\right]+\frac{2}{3} \cdot\left[(1)^{\frac{3}{2}}\right]$ 
= $\frac{2}{3} \cdot\left[(2)^{\frac{3}{2}}-(1)^{\frac{3}{2}}\right]+\frac{2}{3} \cdot\left[(1)^{\frac{3}{2}}\right]$ 
= $\frac{2}{3} \cdot\left[(2)^{\frac{3}{2}}-1\right]+\frac{2}{3} \cdot[1]$ 
= $\frac{2}{3} \cdot[2 \sqrt{2}]$ 
$\Rightarrow$ $I=\frac{4 \sqrt{2}}{3}$  
 

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