Standard +0.3 This is a straightforward binomial expansion question requiring calculation of one term's coefficient using the formula. The 'almost correct' hint guides students to find the error (likely a sign mistake). It's slightly easier than average as it's a standard technique with clear direction, though the error-spotting adds minimal complexity.
Joseph is expanding \((2 - 3x)^7\) in ascending powers of \(x\).
He states that the coefficient of the fourth term is 15120
Joseph's teacher comments that his answer is almost correct.
Using a suitable calculation, explain the teacher's comment.
[4 marks]
Question 5:
5 | Chooses x3 term (PI) | 1.1b | B1 | (35)( 24)(-3)3 x3
–15120x3
Joseph has the right number
but the wrong sign
Uses correct coefficient formula,
allow use of either 7C or 7C (OE)
3 4 | 1.1a | M1
Obtains -15120 or 22680 as the
value of the coefficient (ignore any
power of x if included as part of the
coefficient) | 1.1b | A1F
Obtains -15120 and explains how
the error could have occurred or
what the error is | 2.4 | R1
Total | 4
Q | Marking Instructions | AO | Marks | Typical Solution
Joseph is expanding $(2 - 3x)^7$ in ascending powers of $x$.
He states that the coefficient of the fourth term is 15120
Joseph's teacher comments that his answer is almost correct.
Using a suitable calculation, explain the teacher's comment.
[4 marks]
\hfill \mbox{\textit{AQA AS Paper 2 2020 Q5 [4]}}