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Question
If a + b = 8 and ab = 15, find a3 + b3.
Sum
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Solution
Here, a + b = 8, ab = 15
Using the identity,
a3 + b3 = (a + b)3 − 3ab (a + b)
= (8)3 − 3(15)(8)
= 512 − 3(120)
= 512 − 360
∴ a3 + b3 = 152
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Application of Formulae
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Chapter 3: Expansions - EXERCISE B [Page 35]
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