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Date May 2008 Marks available 2 Reference code 08M.1.sl.TZ2.15
Level SL only Paper 1 Time zone TZ2
Command term Question number 15 Adapted from N/A

Question

The function \(f(x)\) is such that \(f'(x) < 0\) for \(1 < x < 4\). At the point \({\text{P}}(4{\text{, }}2)\) on the graph of \(f(x)\) the gradient is zero.

Write down the equation of the tangent to the graph of \(f(x)\) at \({\text{P}}\).

[2]
a.

State whether \(f(4)\) is greater than, equal to or less than \(f(2)\).

[2]
b.

Given that \(f(x)\) is increasing for \(4 \leqslant x < 7\), what can you say about the point \({\text{P}}\)?

[2]
c.

Markscheme

\(y = 2\).     (A1)(A1)     (C2)

Note: Award (A1) for \(y = \ldots \), (A1) for \(2\).
Accept \(f(x) = 2\) and \(y = 0x + 2\)

a.

Less (than).     (A2)     (C2)

[2 marks]

b.

Local minimum (accept minimum, smallest or equivalent)     (A2)     (C2)

Note: Award (A1) for stationary or turning point mentioned.
No mark is awarded for \({\text{gradient}} = 0\) as this is given in the question.

c.

Examiners report

This question was poorly answered by many of the candidates. They could not write down the equation of the tangent, they could not say whether one value was greater or less than another and they could not answer that \({\text{P}}\) was a minimum point. Most attempted the question so it was not a case that the paper was too long. This was a very good discriminator for the paper.

a.

This question was poorly answered by many of the candidates. They could not write down the equation of the tangent, they could not say whether one value was greater or less than another and they could not answer that \({\text{P}}\) was a minimum point. Most attempted the question so it was not a case that the paper was too long. This was a very good discriminator for the paper.

b.

This question was poorly answered by many of the candidates. They could not write down the equation of the tangent, they could not say whether one value was greater or less than another and they could not answer that \({\text{P}}\) was a minimum point. Most attempted the question so it was not a case that the paper was too long. This was a very good discriminator for the paper.

c.

Syllabus sections

Topic 7 - Introduction to differential calculus » 7.4 » Graphical interpretation of \(f'\left( x \right) > 0\), \(f'\left( x \right) = 0\) and \(f'\left( x \right) < 0\).

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