12 For any positive parameter \(k\), the curve \(C _ { k }\) is defined by the polar equation
\(\mathrm { r } = \mathrm { k } ( \cos \theta + 1 ) + \frac { 10 } { \mathrm { k } } , 0 \leqslant \theta \leqslant 2 \pi\).
For each value of \(k\) the curve is a single, closed loop with no self-intersections. The diagram shows \(C _ { 10.5 }\) for the purpose of illustration.
\includegraphics[max width=\textwidth, alt={}, center]{fbb82fa2-b316-44ae-a19e-197b45f51c87-6_558_723_550_242}
Each curve, \(C _ { k }\), encloses a certain area, \(A _ { k }\).
You are given that there is a single minimum value of \(A _ { k }\).
Determine, in an exact form, the value of \(k\) for which \(C _ { k }\) encloses this minimum area.
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Question 12:
Answer Marks
12 1 2 1 0 2 1 0 2
k ( c o s 1 ) d + + or k ( c o s 1 ) d + +
2 k k
0 0
1 2 ( ) 1 0 1 0 0
k 2 c o s 2 2 c o s 1 + 2 k ( c o s + 1 ) + d = + +
2 k k 2
0
12 k2 10 102
= ( cos2+1 ) +2kk+ cos+k+ d
2 2 k k
0
1 k 2 1 1 0 k 2 1 0 2 2
s i n 2 2 k k s i n k = + + + + +
2 2 2 k 2 k
0
k 2 1 0 k 2 1 0 2
s i n 4 k k s i n 2 2 k = + + + + +
8 k 2 k
3 k 2 1 0 0
2 0 = + +
2 k 2
d 3 k 2 1 0 0 2 0 0
2 0 3 k ( 0 ) + + = − =
k d 2 k 2 k 3
1
2 0 0 4
k =
M1
M1dep*
M1
A1
M1
A1
1.1
1.1
1.1
1.1
2.1a
Answer Marks
1.1 Using 1 r2d with correct expression for r - condone
2
lack of (or incorrect) limits. Condone missing 12 only.
1
Expanding and using correct c o s 2 (1 c o s 2 ) = + -
2
need not be in an integral.
Integrating their k c o s 2 k c o s k d + + correctly
1 2 3
to 1k sin2+k sin+k with k ,k ,k 0
2 1 2 3 1 2 3
Substitute correct limits 0 and 2 - dependent on
previous M mark. Need not see zeros from 0 limit or
other terms that would be zero when evaluated.
cao from correct integral and correct integration.
Condone ( 3 k 2 4 0 2 0 0 k 2 ) + + − from missing 1.
2
Differentiating theirA correctly which must be of the
k
form a k 2 + b + c k − 2 with a , b , c 0 . Dependent on all
previous M marks.
Dependent on all previous marks and no errors. A0 if
correct k obtained but 12 missing from area formula
(unless justified). Accept any exact equivalent.
Condone omission of (or other constant factor)
for final two marks.
PMT
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Copy
Question 12:
12 | 1 2 1 0 2 1 0 2
k ( c o s 1 ) d + + or k ( c o s 1 ) d + +
2 k k
0 0
1 2 ( ) 1 0 1 0 0
k 2 c o s 2 2 c o s 1 + 2 k ( c o s + 1 ) + d = + +
2 k k 2
0
12 k2 10 102
= ( cos2+1 ) +2kk+ cos+k+ d
2 2 k k
0
1 k 2 1 1 0 k 2 1 0 2 2
s i n 2 2 k k s i n k = + + + + +
2 2 2 k 2 k
0
k 2 1 0 k 2 1 0 2
s i n 4 k k s i n 2 2 k = + + + + +
8 k 2 k
3 k 2 1 0 0
2 0 = + +
2 k 2
d 3 k 2 1 0 0 2 0 0
2 0 3 k ( 0 ) + + = − =
k d 2 k 2 k 3
1
2 0 0 4
k =
3 | M1*
M1
M1dep*
M1
A1
M1
A1
[7] | 3.1a
1.1
1.1
1.1
1.1
2.1a
1.1 | Using 1 r2d with correct expression for r - condone
2
lack of (or incorrect) limits. Condone missing 12 only.
1
Expanding and using correct c o s 2 (1 c o s 2 ) = + -
2
need not be in an integral.
Integrating their k c o s 2 k c o s k d + + correctly
1 2 3
to 1k sin2+k sin+k with k ,k ,k 0
2 1 2 3 1 2 3
Substitute correct limits 0 and 2 - dependent on
previous M mark. Need not see zeros from 0 limit or
other terms that would be zero when evaluated.
cao from correct integral and correct integration.
Condone ( 3 k 2 4 0 2 0 0 k 2 ) + + − from missing 1.
2
Differentiating theirA correctly which must be of the
k
form a k 2 + b + c k − 2 with a , b , c 0 . Dependent on all
previous M marks.
Dependent on all previous marks and no errors. A0 if
correct k obtained but 12 missing from area formula
(unless justified). Accept any exact equivalent.
Condone omission of (or other constant factor)
for final two marks.
PMT
Need to get in touch?
If you ever have any questions about OCR qualifications or services (including administration, logistics and teaching) please feel free to get in
touch with our customer support centre.
Call us on
01223 553998
Alternatively, you can email us on
support@ocr.org.uk
For more information visit
ocr.org.uk/qualifications/resource-finder
ocr.org.uk
Twitter/ocrexams
/ocrexams
/company/ocr
/ocrexams
OCR is part of Cambridge University Press & Assessment, a department of the University of Cambridge.
For staff training purposes and as part of our quality assurance programme your call may be recorded or monitored. © OCR
2024 Oxford Cambridge and RSA Examinations is a Company Limited by Guarantee. Registered in England. Registered office
The Triangle Building, Shaftesbury Road, Cambridge, CB2 8EA.
Registered company number 3484466. OCR is an exempt charity.
OCR operates academic and vocational qualifications regulated by Ofqual, Qualifications Wales and CCEA as listed in their
qualifications registers including A Levels, GCSEs, Cambridge Technicals and Cambridge Nationals.
OCR provides resources to help you deliver our qualifications. These resources do not represent any particular teaching method
we expect you to use. We update our resources regularly and aim to make sure content is accurate but please check the OCR
website so that you have the most up-to-date version. OCR cannot be held responsible for any errors or omissions in these
resources.
Though we make every effort to check our resources, there may be contradictions between published support and the
specification, so it is important that you always use information in the latest specification. We indicate any specification changes
within the document itself, change the version number and provide a summary of the changes. If you do notice a discrepancy
between the specification and a resource, please contact us.
Whether you already offer OCR qualifications, are new to OCR or are thinking about switching, you can request more
information using our Expression of Interest form.
Please get in touch if you want to discuss the accessibility of resources we offer to support you in delivering our qualifications.
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12 For any positive parameter $k$, the curve $C _ { k }$ is defined by the polar equation\\
$\mathrm { r } = \mathrm { k } ( \cos \theta + 1 ) + \frac { 10 } { \mathrm { k } } , 0 \leqslant \theta \leqslant 2 \pi$.\\
For each value of $k$ the curve is a single, closed loop with no self-intersections. The diagram shows $C _ { 10.5 }$ for the purpose of illustration.\\
\includegraphics[max width=\textwidth, alt={}, center]{fbb82fa2-b316-44ae-a19e-197b45f51c87-6_558_723_550_242}
Each curve, $C _ { k }$, encloses a certain area, $A _ { k }$.\\
You are given that there is a single minimum value of $A _ { k }$.\\
Determine, in an exact form, the value of $k$ for which $C _ { k }$ encloses this minimum area.
\hfill \mbox{\textit{OCR Further Pure Core 1 2024 Q12 [7]}}