Question

If $x^2+\frac{1}{x^2}=79$ then $x+\frac{1}{x}=$ .........

• A. $\sqrt{75}$
• B. $9$
• C. $\sqrt{79}$
• D. none of these

Answer 1

The correct option is B $9$

Given, $x^2+\frac{1}{x^2}=79$ ...(i)

On squaring $x+\frac{1}{x}$, we get

$(x+\frac{1}{x}{)}^2=x^2+\frac{1}{x^2}+2$

$=79+2=81$ (from (i))

$\Rightarrow x+\frac{1}{x}=\pm 9$

Option B is correct.