Date | May 2012 | Marks available | 3 | Reference code | 12M.1.hl.TZ1.6 |
Level | HL only | Paper | 1 | Time zone | TZ1 |
Command term | Find | Question number | 6 | Adapted from | N/A |
Question
The graph below shows the two curves \(y = \frac{1}{x}\) and \(y = \frac{k}{x}\), where \(k > 1\).
Find the area of region A in terms of k .
Find the area of region B in terms of k .
Find the ratio of the area of region A to the area of region B .
Markscheme
\(\int_{\frac{1}{6}}^1 {\frac{k}{x} - \frac{1}{x}{\text{d}}x = (k - 1} )[\ln x]_{\frac{1}{6}}^1\) M1 A1
Note: Award M1 for \(\int {\frac{k}{x} - \frac{1}{x}{\text{d}}x{\text{ or }}\int {\frac{1}{x} - \frac{k}{x}{\text{d}}x} } \) and A1 for \((k - 1)\ln x\) seen in part (a) or later in part (b).
\( = (1 - k)\ln \frac{1}{6}\) A1
[3 marks]
\(\int_1^{\sqrt 6 } {\frac{k}{x} - \frac{1}{x}{\text{d}}x = (k - 1} )[\ln x]_1^{\sqrt 6 }\) (A1)
Note: Award A1 for correct change of limits.
\( = (k - 1)\ln \sqrt 6 \) A1
[2 marks]
\((1 - k)\ln \frac{1}{6} = (k - 1)\ln 6\) A1
\((k - 1)\ln \sqrt 6 = \frac{1}{2}(k - 1)\ln 6\) A1
Note: This simplification could have occurred earlier, and marks should still be awarded.
ratio is 2 (or 2:1) A1
[3 marks]
Examiners report
Generally well answered by most candidates. Basic algebra sometimes let students down in the simplification of the ratio in part (c). It was not uncommon to see \(\frac{{\log A}}{{\log B}}\) simplified to \(\frac{A}{B}\).
Generally well answered by most candidates. Basic algebra sometimes let students down in the simplification of the ratio in part (c). It was not uncommon to see \(\frac{{\log A}}{{\log B}}\) simplified to \(\frac{A}{B}\).
Generally well answered by most candidates. Basic algebra sometimes let students down in the simplification of the ratio in part (c). It was not uncommon to see \(\frac{{\log A}}{{\log B}}\) simplified to \(\frac{A}{B}\).