Date | May 2010 | Marks available | 6 | Reference code | 10M.2.sl.TZ2.4 |
Level | SL only | Paper | 2 | Time zone | TZ2 |
Command term | Find | Question number | 4 | Adapted from | N/A |
Question
Find the term in x4 in the expansion of (3x2−2x)5 .
Markscheme
evidence of substituting into binomial expansion (M1)
e.g. a5+(51)a4b+(52)a3b2+…
identifying correct term for x4 (M1)
evidence of calculating the factors, in any order A1A1A1
e.g. (52),27x6,4x2 ; 10(3x2)3(−2x)2
Note: Award A1 for each correct factor.
term=1080x4 A1 N2
Note: Award M1M1A1A1A1A0 for 1080 with working shown.
[6 marks]
Examiners report
Although a great number of students recognized they could use the binomial theorem, fewer were successful in finding the term in x4 .
Candidates showed various difficulties when trying to solve this problem:
- choosing the incorrect term
- attempting to expand (3x2−2x)5 by hand
- finding only the coefficient of the term
- not being able to determine which term would yield an x4
- errors in the calculations of the coefficient.