Find the $x$-coordinate of P.

Find $f(x)$, expressing your answer as a single logarithm.

The graph of $f$ is transformed by a vertical stretch with scale factor $\frac{1}{{\ln 3}}$. The image of P under this transformation has coordinates $(a,{\text{ }}b)$.

Find the value of $a$ and of $b$, where $a,{\text{ }}b \in \mathbb{N}$.

recognizing $f'(x) = 0$     (M1)

correct working     (A1)

eg$\,\,\,\,\,$$6 - 2x = 0$

$x = 3$    A1     N2

[3 marks]

evidence of integration     (M1)

eg$\,\,\,\,\,$$\int {f',{\text{ }}\int {\frac{{6 - 2x}}{{6x - {x^2}}}{\text{d}}x} }$

using substitution     (A1)

eg$\,\,\,\,\,$$\int {\frac{1}{u}{\text{d}}u}$ where $u = 6x - {x^2}$

correct integral     A1

eg$\,\,\,\,\,$$\ln (u) + c,{\text{ }}\ln (6x - {x^2})$

substituting $(3,{\text{ }}\ln 27)$ into their integrated expression (must have $c$)     (M1)

eg$\,\,\,\,\,$$\ln (6 \times 3 - {3^2}) + c = \ln 27,{\text{ }}\ln (18 - 9) + \ln k = \ln 27$

correct working     (A1)

eg$\,\,\,\,\,$$c = \ln 27 - \ln 9$

EITHER

$c = \ln 3$    (A1)

attempt to substitute their value of $c$ into $f(x)$     (M1)

eg$\,\,\,\,\,$$f(x) = \ln (6x - {x^2}) + \ln 3$     A1     N4

OR

attempt to substitute their value of $c$ into $f(x)$     (M1)

eg$\,\,\,\,\,$$f(x) = \ln (6x - {x^2}) + \ln 27 - \ln 9$

correct use of a log law     (A1)

eg$\,\,\,\,\,$$f(x) = \ln (6x - {x^2}) + \ln \left( {\frac{{27}}{9}} \right),{\text{ }}f(x) = \ln \left( {27(6x - {x^2})} \right) - \ln 9$

$f(x) = \ln \left( {3(6x - {x^2})} \right)$    A1     N4

[8 marks]

$a = 3$    A1     N1

correct working     A1

eg$\,\,\,\,\,$$\frac{{\ln 27}}{{\ln 3}}$

correct use of log law     (A1)

eg$\,\,\,\,\,$$\frac{{3\ln 3}}{{\ln 3}},{\text{ }}{\log _3}27$

$b = 3$    A1     N2

[4 marks]

Part a) was well answered.

In part b) most candidates realised that integration was required but fewer recognised the need to use integration by substitution. Quite a number of candidates who integrated correctly omitted finding the constant of integration.

In part c) many candidates showed good understanding of transformations and could apply them correctly, however, correct use of the laws of logarithms was challenging for many. In particular, a common error was $\frac{{\ln 27}}{{\ln 3}} = \ln 9$.