MCQ
$\int\limits_{\frac{\pi }{4}}^{\frac{\pi }{2}} {{{\left( {2\cos ec\,\,x} \right)}^{17}}\,dx = ..........} $
  • $\int\limits_0^{\log \left( {1 + \sqrt 2 } \right)} {2{{\left( {{e^u} + {e^{ - u}}} \right)}^{16}}du} $
  • B
    $\int\limits_0^{\log \left( {1 + \sqrt 2 } \right)} {{{\left( {{e^u} + {e^{ - u}}} \right)}^{17}}du} $
  • C
    $\int\limits_0^{\log \left( {1 + \sqrt 2 } \right)} {{{\left( {{e^u} - {e^{ - u}}} \right)}^{17}}du} $
  • D
    $\int\limits_0^{\log \left( {1 + \sqrt 2 } \right)} {2{{\left( {{e^u} - {e^{ - u}}} \right)}^{16}}du} $

Answer

Correct option: A.
$\int\limits_0^{\log \left( {1 + \sqrt 2 } \right)} {2{{\left( {{e^u} + {e^{ - u}}} \right)}^{16}}du} $
A

$I=\int_{\frac{\pi}{4}}^{\frac{\pi}{2}} (2\cos ecx)^{17}dx$

$=\int_{\frac{\pi}{4}}^{\frac{\pi}{2}} 2^{17}(2\cos ecx)^{16}\cos ecx \ dx$

અહી,$\cos ecx+\cot x=t$

=$-\cos ecxdx=\frac{dt}{\cos ecx+\cot x}$

તથા

$\begin{cases}x=\frac{\pi}{4}\Rightarrow &t=\sqrt{2}+1\\x=\frac{\pi}{2}\Rightarrow &t=1\end{cases}$

$I=\int_{\sqrt{2}+1}^{'} -2^{17}\left(\frac{t+\frac{1}{t}}{2}\right)^{16}\frac{dt}{t}$

અહી$t=e^u$

$at=e^udu$

$\begin{cases}t=1, & u = 0\\t=\sqrt{2}+1, &u=\log(\sqrt{2}+1)\end{cases}$

$I=-\int_{\log\sqrt{2}+1}^{0} 2(e^u+e^{-u})^{16}\frac{e^udu}{e^u}$.

$I=\int_{\log\sqrt{2}+1}^{0} 2(e^u+e^{-u})^{16}du$

$I=\int_{0}^{\log\sqrt{2}+1} 2(e^u+e^{-u})^{16}du$

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