Q42 / 90 · KVPY 2011 (SB/SX) · Mathematics

Let $[x]$ denote the largest integer not exceeding $x$ and $\{x\}=x-[x]$. Then $\int_{0}^{2012} \frac{e^{\cos (\pi\{x\})}}{e^{\cos (\pi\{x\})}+e^{-\cos (\pi\{x\})}} d x$ is equal to -

  • A
    0
  • Correct answer
    B
    1006
  • C
    2012
  • D
    $2012 \pi$

Solution

$\mathrm{I}=2012 \int_{0}^{1} \frac{e^{\cos \pi x}}{e^{\cos \pi x}+e^{-\cos \pi x}} d x$ using king property $\mathrm{I}=2012 \int_{0}^{1} \frac{e^{-\cos \pi x}}{e^{-\cos \pi x}+e^{\cos \pi x}} d x \Rightarrow 2 \mathrm{I}=2012 \Rightarrow \mathrm{I}=1006$

Hence, the correct answer is option: 'B'.

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