Question

The rationalising factor for rationalization of the denominator of $\frac{21\sqrt{5}}{\sqrt{7}}$ is

• A. $\sqrt{5}$
• B. $\sqrt{7}$
• C. $\sqrt{35}$
• D. $\sqrt{21}$

Answer 1

The correct option is B $\sqrt{7}$

Case 1:
$\frac{21\sqrt{5}}{\sqrt{7}}\times \frac{\sqrt{7}}{\sqrt{7}}=\frac{21\sqrt{35}}{\sqrt{49}}=\frac{21\sqrt{35}}{7}$

denominator of the fraction i.e. 7 is a rational number.

Hence, the rationalising factor for rationalizing the denominator is $\sqrt{7}$