If $\mathrm{x}$ is so small that $\mathrm{x}^3$ and higher powers of $\mathrm{x}$ may be neglected, then…

If $\mathrm{x}$ is so small that $\mathrm{x}^3$ and higher powers of $\mathrm{x}$ may be neglected, then $\frac{(1+x)^{3 / 2}-\left(1+\frac{1}{2} x\right)^3}{(1-x)^{1 / 2}}$
  1. $1-\frac{3}{8} x^2$
  2. $3 x+\frac{3}{8} x^2$
  3. $-\frac{3}{8} x^2$
  4. $\frac{x}{2}-\frac{3}{8} x^2$

Solution

$ \begin{aligned} & (1-x)^{1 / 2}\left[1+\frac{3}{2} x+\frac{3}{2}\left(\frac{3}{2}-1\right) x^2-1-3\left(\frac{1}{2} x\right)-3(2)\left(\frac{1}{2} x\right)^2\right] \\ & =(1-x)^{1 / 2}\left[-\frac{3}{8} x^2\right]=-\frac{3}{8} x^2 \end{aligned} $

Asked in: JEE Main 2005

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