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Question
If a+b=5 and ab = 6, find a2 + b2
Sum
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Solution
(a + b)2 = a2 + b2 + 2ab
⇒ (5)2 = a2 + b2 + 2×6
⇒ 25 = a2 + b2 + 12
⇒ 25 − 12 = a2 + b2
⇒ 13 = a2 + b2
∴ a2 + b2 = 13
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