You multiply top and bottom of the fraction by the conjugate of 5 - √2 which is 5 + √2. This produces a rational denominator:-
= √7 ( 5 + √2) / (5 - √2)(5 + √2)
= √7 ( 5 + √2) / (25 -2)
= (√7 ( 5 + √2)) / 23 answer
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