CAIE FP1 2006 November — Question 6 9 marks

Exam BoardCAIE
ModuleFP1 (Further Pure Mathematics 1)
Year2006
SessionNovember
Marks9
PaperDownload PDF ↗
TopicRoots of polynomials
TypeEquation with nonlinearly transformed roots
DifficultyChallenging +1.2 This is a standard Further Pure 1 question on transformed roots requiring systematic application of Vieta's formulas and algebraic manipulation. While it involves multiple steps (finding the transformation, determining p and q, then computing power sums), the techniques are well-established and follow a predictable pattern. The transformation y = (4x+1)/(x+1) leads to a cubic that students practice regularly, and computing power sums from the resulting equation is a routine extension. More challenging than average A-level due to being Further Maths content and requiring careful algebra, but not requiring novel insight.
Spec4.05a Roots and coefficients: symmetric functions4.05b Transform equations: substitution for new roots

6 The roots of the equation $$x ^ { 3 } + x + 1 = 0$$ are \(\alpha , \beta , \gamma\). Show that the equation whose roots are $$\frac { 4 \alpha + 1 } { \alpha + 1 } , \quad \frac { 4 \beta + 1 } { \beta + 1 } , \quad \frac { 4 \gamma + 1 } { \gamma + 1 }$$ is of the form $$y ^ { 3 } + p y + q = 0$$ where the numbers \(p\) and \(q\) are to be determined. Hence find the value of $$\left( \frac { 4 \alpha + 1 } { \alpha + 1 } \right) ^ { n } + \left( \frac { 4 \beta + 1 } { \beta + 1 } \right) ^ { n } + \left( \frac { 4 \gamma + 1 } { \gamma + 1 } \right) ^ { n }$$ for \(n = 2\) and for \(n = 3\).

6 The roots of the equation

$$x ^ { 3 } + x + 1 = 0$$

are $\alpha , \beta , \gamma$. Show that the equation whose roots are

$$\frac { 4 \alpha + 1 } { \alpha + 1 } , \quad \frac { 4 \beta + 1 } { \beta + 1 } , \quad \frac { 4 \gamma + 1 } { \gamma + 1 }$$

is of the form

$$y ^ { 3 } + p y + q = 0$$

where the numbers $p$ and $q$ are to be determined.

Hence find the value of

$$\left( \frac { 4 \alpha + 1 } { \alpha + 1 } \right) ^ { n } + \left( \frac { 4 \beta + 1 } { \beta + 1 } \right) ^ { n } + \left( \frac { 4 \gamma + 1 } { \gamma + 1 } \right) ^ { n }$$

for $n = 2$ and for $n = 3$.

\hfill \mbox{\textit{CAIE FP1 2006 Q6 [9]}}