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Question
If a + b = 9 and ab = 18, find a − b.
Sum
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Solution
Here, a + b = 9, ab = 18
Thus,
(9)2 − (a − b)2 = 4 × 18 ...[Using (a + b)2 − (a − b)2 = 4ab]
81 − (a − b)2 = 72
(a − b)2 = 81 − 72
∴ (a − b)2 = 9
∴ a − b = `± sqrt9`
∴ a − b = ± 3
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