AQA Further AS Paper 1 Specimen — Question 11 5 marks

Exam BoardAQA
ModuleFurther AS Paper 1 (Further AS Paper 1)
SessionSpecimen
Marks5
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicRoots of polynomials
TypeComplex roots with real coefficients
DifficultyChallenging +1.2 This is a Further Maths question requiring knowledge that complex roots come in conjugate pairs, use of Vieta's formulas, and geometric interpretation on an Argand diagram. While it involves multiple concepts (polynomial roots, complex conjugates, area calculation), the solution path is relatively standard once you recognize that β and γ must be conjugate pairs of form 2±bi. The area condition gives b=4, then Vieta's formulas yield c and d directly. More routine than typical Further Maths proof questions but requires synthesis of several ideas.
Spec4.02k Argand diagrams: geometric interpretation4.05a Roots and coefficients: symmetric functions

11 The equation \(x ^ { 3 } - 8 x ^ { 2 } + c x + d = 0\) where \(c\) and \(d\) are real numbers, has roots \(\alpha , \beta , \gamma\).
When plotted on an Argand diagram, the triangle with vertices at \(\alpha , \beta , \gamma\) has an area of 8 . Given \(\alpha = 2\), find the values of \(c\) and \(d\). Fully justify your solution.
[0pt] [5 marks]

Question 11:
AnswerMarks Guidance
AnswerMark Guidance
Real coefficients \(\Rightarrow \beta = p + qi\) and \(\gamma = p - qi\)B1 Seen anywhere in solution
\(\alpha + \beta + \gamma = 8 \Rightarrow 2 + p + qi + p - qi = 8 \Rightarrow p = 3\)M1 Uses sum of roots \(= -b/a\) with conjugate pair to find real part \(p\)
\((p-2)q = 8 \Rightarrow q = 8\)M1 Uses \((p-2)\) and area of triangle on Argand diagram to find imaginary parts
\(\beta = 3 + 8i\) and \(\gamma = 3 - 8i\)M1 Correct method to find \(c\) or \(d\) using their \(p \pm qi\)
\(d = -\alpha\beta\gamma = -146\); \(c = \sum\alpha\beta = 85\)A1 Both correct; CAO
## Question 11:

| Answer | Mark | Guidance |
|--------|------|----------|
| Real coefficients $\Rightarrow \beta = p + qi$ and $\gamma = p - qi$ | B1 | Seen anywhere in solution |
| $\alpha + \beta + \gamma = 8 \Rightarrow 2 + p + qi + p - qi = 8 \Rightarrow p = 3$ | M1 | Uses sum of roots $= -b/a$ with conjugate pair to find real part $p$ |
| $(p-2)q = 8 \Rightarrow q = 8$ | M1 | Uses $(p-2)$ and area of triangle on Argand diagram to find imaginary parts |
| $\beta = 3 + 8i$ and $\gamma = 3 - 8i$ | M1 | Correct method to find $c$ or $d$ using their $p \pm qi$ |
| $d = -\alpha\beta\gamma = -146$; $c = \sum\alpha\beta = 85$ | A1 | Both correct; CAO |
11 The equation $x ^ { 3 } - 8 x ^ { 2 } + c x + d = 0$ where $c$ and $d$ are real numbers, has roots $\alpha , \beta , \gamma$.\\
When plotted on an Argand diagram, the triangle with vertices at $\alpha , \beta , \gamma$ has an area of 8 .

Given $\alpha = 2$, find the values of $c$ and $d$.

Fully justify your solution.\\[0pt]
[5 marks]

\hfill \mbox{\textit{AQA Further AS Paper 1  Q11 [5]}}