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Date May 2012 Marks available 2 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 .

[3]
a.

Find the area of region B in terms of k .

[2]
b.

Find the ratio of the area of region A to the area of region B .

[3]
c.

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]

a.

\(\int_1^{\sqrt 6 } {\frac{k}{x} - \frac{1}{x}{\text{d}}x = (k - 1} )[\ln x]_1^{\sqrt 6 }\)     (A1)

Note: Award A1 for correct change of limits.

 

\( = (k - 1)\ln \sqrt 6 \)     A1

[2 marks]

b.

\((1 - k)\ln \frac{1}{6} = (k - 1)\ln 6\)     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] 

 

c.

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 \(\frac{A}{B}\).

a.

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 \(\frac{A}{B}\).

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 \(\frac{A}{B}\).

c.

Syllabus sections

Topic 6 - Core: Calculus » 6.5 » Area of the region enclosed by a curve and the \(x\)-axis or \(y\)-axis in a given interval; areas of regions enclosed by curves.
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