MCQ
ધારો કે $f(x)=\int \frac{2 x}{\left(x^2+1\right)\left(x^2+3\right)} d x$. જો $f(3)=\frac{1}{2}\left(\log _e 5-\log _e 6\right)$ હોય,તો $f(4)=............$
  • $\frac{1}{2}\left(\log _e 17-\log _e 19\right)$
  • B
    $\log _e 17-\log _e 18$
  • C
    $\frac{1}{2}\left(\log _{ e } 19-\log _{ e } 17\right)$
  • D
    $\log _e 19-\log _e 20$

Answer

Correct option: A.
$\frac{1}{2}\left(\log _e 17-\log _e 19\right)$
a
Put $x ^2= t$

$\int \frac{d t}{(t+1)(t+3)}=\frac{1}{2} \int\left(\frac{1}{t+1}-\frac{1}{t+3}\right) d t$

$f(x)=\frac{1}{2} \ln \left(\frac{x^2+1}{x^2+3}\right)+C$

$f(3)=\frac{1}{2}(\ln 10-\ln 12)+C$

$\Rightarrow C=0$

$f(4)=\frac{1}{2} \ln \left(\frac{17}{19}\right)$

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