First, simply the fraction \(\displaystyle \frac{{\sqrt {x^2 - 5} - \sqrt {\left( {x + h} \right)^2 - 5} }}{{h\left( {\sqrt {x^2 - 5} } \right)\left( {\sqrt {\left( {x + h} \right)^2 - 5} } \right)}}\).
Then rationalize by multiplying numerator and denominator by \(\displaystyle \sqrt {x^2 - 5} + \sqrt {\left( {x + h} \right)^2 - 5}\)
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