Moderate -0.3 This is a straightforward binomial expansion requiring identification of the correct term where powers of x sum to 1. It's slightly easier than average because it's a single-step problem with clear method (general term formula), though students must be careful with the negative power arithmetic.
\(^7C_3 x^3 \left(\frac{2}{x^2}\right)^2\) SOI and leading to final answer
B2
B1 for 2/3 parts correct leading to ans.
84 or 84x as final answer
B1
If no answer; 84x seen scores B2, else \(^7C_3 x^5 \left(\frac{2}{x^2}\right)\) scores SCB1 only
$^7C_3 x^3 \left(\frac{2}{x^2}\right)^2$ SOI and leading to final answer | B2 | B1 for 2/3 parts correct leading to ans.
84 or 84x as final answer | B1 | If no answer; 84x seen scores B2, else $^7C_3 x^5 \left(\frac{2}{x^2}\right)$ scores SCB1 only
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