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# P2 Question watch

1. Given that x + 1/x = 3

Expand (x+1/x)^3 and use your expression to show that:

x^3 + 1/x^3 = 18

I did the expansion: x^3 + 3x+3x^-1 + x^-3, but I don't know how to do the second bit. Thanks for any help.
2. 3^3 = x^3 + 3x+3x^-1 + x^-3 = 3(x+1/x) + x^3 + 1/x^3 = 27

The first bracket is the same as the original expression which equals 3., so you get
27 = 3(3) + x^3 + 1/x^3
18 = x^3 + 1/x^3

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