Easy -1.2 This is a straightforward application of the binomial theorem with n=3 (a small positive integer), requiring only direct expansion and simplification of algebraic terms. The presence of 1/x adds minimal complexity compared to standard binomial expansions, and with only 4 terms to compute, this is a routine C1-level exercise testing basic recall and algebraic manipulation.
B1 for both \(x^3\) and \(\frac{125}{x^3}\) or \(125x^{-3}\) isw; and M1 for 1 3 3 1 soi; A1 for each of \(15x\) and \(\frac{75}{x}\) or \(75x^{-1}\) isw; or SC2 for completely correct unsimplified answer
## Question 10:
$x^3 + 15x + \frac{75}{x} + \frac{125}{x^3}$ www isw, or $x^3 + 15x + 75x^{-1} + 125x^{-3}$ www isw | **B4** | **B1** for both $x^3$ and $\frac{125}{x^3}$ or $125x^{-3}$ isw; and **M1** for 1 3 3 1 soi; **A1** for each of $15x$ and $\frac{75}{x}$ or $75x^{-1}$ isw; or **SC2** for completely correct unsimplified answer
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