Find the coefficient of x in the expansion of (2x - 1/x)^5.
- (i)Find the coefficient of x in the expansion of (2x - 1/x)^5.[2]
- (ii)Hence find the coefficient of x in the expansion of (1 + 3x²) (2x - 1/x)^5.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- Coefficient of x = 80(x)
- [B2] Correct value must be selected for both marks. SR +80 seen in an expansion gets B1 or -80 gets B1 if selected.
- Coefficient of 1/x = -40
- [B2] Correct value soi in (ii), if powers unsimplified only allow if selected. SR +40 soi in (ii) gets B1.
- Coefficient of x = (1 × their 80) + (3 ×their - 40) = -40(x)
- [M1 A1] Links the appropriate 2 terms only for M1.
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