If $[x]$ is the greatest integer $\leq x$, then the value of the integral $\int_{-0.9}^{0…

If $[x]$ is the greatest integer $\leq x$, then the value of the integral $\int_{-0.9}^{0.9}\left(\left[x^2\right]+\log \left(\frac{2-x}{2+x}\right)\right) d x$ is
  1. $0.486$
  2. $0.243$
  3. $1.8$
  4. 0

Solution

$ \text { } \begin{aligned} & \int_{-0.9}^{0.9}\left\{\left[x^2\right]+\log \left(\frac{2-x}{2+x}\right)\right\} d x \\ = & \int_{-0.9}^{0.9}\left[x^2\right] d x+\int_{-0.9}^{0.9} \log \left(\frac{2-x}{2+x}\right) d x \end{aligned} $ $ \begin{aligned} & =0+\int_{-0.9}^{0.9} \log \left(\frac{2-x}{2+x}\right) d x \\ & \text { Put } x=-x \Rightarrow f(x)=\log \frac{2-x}{2+x} \\ & \text { and } f(-x)=\log \frac{2+x}{2-x} \\ & =-\log \frac{(2-x)}{2+x}=-f(x) \end{aligned} $ So, it is an odd function, hence Required integral $=0$

Asked in: JEE Main 2012 (26 May Online)

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