Chapter 10 - Section 10.5 - Rationalizing Numerators and Denominators of Radical Expressions - Exercise Set - Page 718: 63

$\sqrt 7$ must be multiplied by $\sqrt 7$ to make the denominator 7, a rational number. When either the numerator or the denominator is multiplied by a particular factor, the other number must be multiplied by the same factor to make sure that the numerical value of the fraction does not change.

When either the numerator or the denominator is multiplied by a particular factor, the other number must be multiplied by the same factor to make sure that the numerical value of the fracion does not change.