When the fraction is rewritten so that its denominator is rational

MATHEMATICS · Single correct · AoPS · Mathematics · Special Factorizations · Special Factorizations

Problem

When the fraction

\dfrac{1}{\sqrt{7}+\sqrt{5}}

is rewritten so that its denominator is rational, what value will appear in the new denominator? (a)

35

(b)

12

(c)

2

(d)

4