Question 348412
{{{(sqrt(c)-sqrt(d))/(sqrt(c)+sqrt(d))}}}
The object is to get the radicals out of the denominator.
Multiply NUM and DEN by the conjugate of the DEN, {{{(sqrt(c)-sqrt(d))}}} 
= {{{(sqrt(c)-sqrt(d))*(sqrt(c)-sqrt(d))/((sqrt(c)+sqrt(d))*(sqrt(c)-sqrt(d)))}}}
= {{{(sqrt(c)-sqrt(d))*(sqrt(c)-sqrt(d))/(c-d)}}}
= {{{(sqrt(c)-sqrt(d))^2/(c-d)}}}
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Or,
= {{{(c + d - 2sqrt(cd))/(c-d)}}}
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Which is simpler is up for debate.