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  1. If a + b = 1 and a3 + b3 + 3ab = k, then the value of k is
    1. 1
    2. 3
    3. 5
    4. 7
Correct Option: A

Using Rule 8,
a + b = 1
Cubing both sides,
(a + b)3 = 13 = 1
⇒ a3 + b3 + 3ab(a + b ) = 1
⇒ a3 + b3 + 3ab = 1 = k
⇒ k = 1


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