How to integrate $\int_0^1 x \log (1 + 2x)dx$ ~~~~~[NCERT Exemp. Q. 45,Page 166 ]

Let $I = \int_0^1 x \log (1 + 2x)dx$


$ = \left[ {\log (1 + 2x)\frac{{{x^2}}}{2}} \right]_0^1 – \int {\frac{1}{{1 + 2x}}} \cdot 2 \cdot \frac{{{x^2}}}{2}dx$


$ = \frac{1}{2}\left[ {{x^2}\log (1 + 2x)} \right]_0^1 – \int {\frac{{{x^2}}}{{1 + 2x}}} dx$


$ = \frac{1}{2}[\log 3 – 0] – \left[ {\int_0^1 {\left( {\frac{x}{2} – \frac{{\frac{x}{2}}}{{1 + 2x}}} \right)} dx} \right]$


$ = \frac{1}{2}\log 3 – \frac{1}{2}\int_0^1 x dx + \frac{1}{2}\int_0^1 {\frac{x}{{1 + 2x}}} dx$


$ = \frac{1}{2}[\log 3 – 0] – \left[ {\int_0^1 {\left( {\frac{x}{2} – \frac{{\frac{x}{2}}}{{1 + 2x}}} \right)} dx} \right]$


$ = \frac{1}{2}\log 3 – \frac{1}{2}\int_0^1 x dx + \frac{1}{2}\int_0^1 {\frac{x}{{1 + 2x}}} dx$


$ = \frac{1}{2}\log 3 – \frac{1}{2}\left[ {\frac{{{x^2}}}{2}} \right]_0^1 + \frac{1}{2}\int_0^1 {\frac{{\frac{1}{2}(2x + 1 – 1)}}{{(2x + 1)}}} dx$


$ = \frac{1}{2}\log 3 – \frac{1}{2}\left[ {\frac{1}{2} – 0} \right] + \frac{1}{4}\int_0^1 d x – \frac{1}{4}\int_0^1 {\frac{1}{{1 + 2x}}} dx$


$ = \frac{1}{2}\log 3 – \frac{1}{4} + \frac{1}{4}[x]_0^1 – \frac{1}{8}[\log |(1 + 2x)|]_0^1$
$ = \frac{1}{2}\log 3 – \frac{1}{4} + \frac{1}{4} – \frac{1}{8}[\log 3 – \log 1]$


$ = \frac{1}{2}\log 3 – \frac{1}{8}\log 3$


$ = \frac{3}{8}\log 3$

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