rationalise the denominator 39/ 7 root 2 - 2 root 5
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39/(7√2 - 2√5)
= 39/(7√2 - 2√5) × (7√2 + 2√5)/(7√2 + 2√5)
= 39(7√2 + 2√5) / (7√2 - 2√5)(7√2 + 2√5)
= (273√2 + 78√5) / (7√2)² - (2√5)²
= (273√2 + 78√5) / (49 × 2) - (4 × 5)
= (273√2 + 78√5) / (98 - 20)
= (273√2 + 78√5) / 78
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