If a3 + b3 = 72 and ab = 8, then what is the value of a + b?
1). 2
2). 5
3). 6
4). 3
Since we can see that a3 + b3 = 72 = 64 + 8 = 43 + 23
⇒ a = 4 and b = 2, this also satisfies ab = 8
∴ the value of a + b is 6 (4 + 2)
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