Question

Coefficient of $x^2$ in the expansion of $(x-\frac{1}{2x})$is?

• A. $\frac{1}{7}$
• B. $\frac{2}{7}$
• C. -7
• D. 7

Answer 1

Answer: (B)

$\frac{2}{7}$

Consider the given function:

$Cofficientof{x}^{2}inthe\exp ansionof(x-\frac{1}{2x})$

$=lettheterms{}^9{C}_r{\left(x\right)}^{9-r}{\left(\frac{1}{2x}\right)}^r$

${\left(x\right)}^{9-r}{\left(x^{-1}\right)}^r=x^2$

$x^{9-r-r}=x^2$

$x^{9-2r}=x^2$

$2r=7$

$r=\frac{2}{7}$

Hence this is the answer.