Edexcel AEA 2012 June — Question 5 14 marks

Exam BoardEdexcel
ModuleAEA (Advanced Extension Award)
Year2012
SessionJune
Marks14
PaperDownload PDF ↗
TopicLaws of Logarithms
TypeIdentify errors in student work
DifficultyChallenging +1.8 This AEA question requires students to work with incorrect logarithm rules, set up equations, solve quadratics in log form, and derive a general result. While conceptually interesting and requiring algebraic manipulation across multiple parts, the individual steps are methodical rather than requiring deep insight. The constraint handling and series summation are standard A-level techniques, though the context of analyzing errors adds modest complexity.
Spec1.06c Logarithm definition: log_a(x) as inverse of a^x1.06f Laws of logarithms: addition, subtraction, power rules

5.[In this question the values of \(a , x\) ,and \(n\) are such that \(a\) and \(x\) are positive real numbers,with \(a > 1 , x \neq a , x \neq 1\) and \(n\) is an integer with \(n > 1\) ] Sam was confused about the rules of logarithms and thought that $$\log _ { a } x ^ { n } = \left( \log _ { a } x \right) ^ { n }$$
  1. Given that \(x\) satisfies statement(1)find \(x\) in terms of \(a\) and \(n\) . Sam also thought that $$\log _ { a } x + \log _ { a } x ^ { 2 } + \ldots + \log _ { a } x ^ { n } = \log _ { a } x + \left( \log _ { a } x \right) ^ { 2 } + \ldots + \left( \log _ { a } x \right) ^ { n }$$
  2. For \(n = 3 , x _ { 1 }\) and \(x _ { 2 } \left( x _ { 1 } > x _ { 2 } \right)\) are the two values of \(x\) that satisfy statement(2).
    1. Find,in terms of \(a\) ,an expression for \(x _ { 1 }\) and an expression for \(x _ { 2 }\) .
    2. Find the exact value of \(\log _ { a } \left( \frac { x _ { 1 } } { x _ { 2 } } \right)\) .
  3. Show that if \(\log _ { a } x\) satisfies statement(2)then $$2 \left( \log _ { a } x \right) ^ { n } - n ( n + 1 ) \log _ { a } x + \left( n ^ { 2 } + n - 2 \right) = 0$$

5.[In this question the values of $a , x$ ,and $n$ are such that $a$ and $x$ are positive real numbers,with $a > 1 , x \neq a , x \neq 1$ and $n$ is an integer with $n > 1$ ]

Sam was confused about the rules of logarithms and thought that

$$\log _ { a } x ^ { n } = \left( \log _ { a } x \right) ^ { n }$$
\begin{enumerate}[label=(\alph*)]
\item Given that $x$ satisfies statement(1)find $x$ in terms of $a$ and $n$ .

Sam also thought that

$$\log _ { a } x + \log _ { a } x ^ { 2 } + \ldots + \log _ { a } x ^ { n } = \log _ { a } x + \left( \log _ { a } x \right) ^ { 2 } + \ldots + \left( \log _ { a } x \right) ^ { n }$$
\item For $n = 3 , x _ { 1 }$ and $x _ { 2 } \left( x _ { 1 } > x _ { 2 } \right)$ are the two values of $x$ that satisfy statement(2).
\begin{enumerate}[label=(\roman*)]
\item Find,in terms of $a$ ,an expression for $x _ { 1 }$ and an expression for $x _ { 2 }$ .
\item Find the exact value of $\log _ { a } \left( \frac { x _ { 1 } } { x _ { 2 } } \right)$ .
\end{enumerate}\item Show that if $\log _ { a } x$ satisfies statement(2)then

$$2 \left( \log _ { a } x \right) ^ { n } - n ( n + 1 ) \log _ { a } x + \left( n ^ { 2 } + n - 2 \right) = 0$$
\end{enumerate}

\hfill \mbox{\textit{Edexcel AEA 2012 Q5 [14]}}