AQA C4 (Core Mathematics 4) 2013 January

1 The polynomial \(\mathrm { f } ( x )\) is defined by \(\mathrm { f } ( x ) = 2 x ^ { 3 } + x ^ { 2 } - 8 x - 7\).

1. Use the Remainder Theorem to find the remainder when \(\mathrm { f } ( x )\) is divided by \(( 2 x + 1 )\).
   (2 marks)
2. The polynomial \(\mathrm { g } ( x )\) is defined by \(\mathrm { g } ( x ) = \mathrm { f } ( x ) + d\), where \(d\) is a constant.
   1. Given that \(( 2 x + 1 )\) is a factor of \(\mathrm { g } ( x )\), show that \(\mathrm { g } ( x ) = 2 x ^ { 3 } + x ^ { 2 } - 8 x - 4\).
      (1 mark)
   2. Given that \(\mathrm { g } ( x )\) can be written as \(\mathrm { g } ( x ) = ( 2 x + 1 ) \left( x ^ { 2 } + a \right)\), where \(a\) is an integer, express \(\mathrm { g } ( x )\) as a product of three linear factors.
   3. Hence, or otherwise, show that \(\frac { \mathrm { g } ( x ) } { 2 x ^ { 3 } - 3 x ^ { 2 } - 2 x } = p + \frac { q } { x }\), where \(p\) and \(q\) are integers.
      (3 marks)

2 It is given that \(\mathrm { f } ( x ) = \frac { 7 x - 1 } { ( 1 + 3 x ) ( 3 - x ) }\).

1. Express \(\mathrm { f } ( x )\) in the form \(\frac { A } { 3 - x } + \frac { B } { 1 + 3 x }\), where \(A\) and \(B\) are integers.
   (3 marks)
2. 1. Find the first three terms of the binomial expansion of \(\mathrm { f } ( x )\) in the form \(a + b x + c x ^ { 2 }\), where \(a\), \(b\) and \(c\) are rational numbers.
      (7 marks)
   2. State why the binomial expansion cannot be expected to give a good approximation to \(\mathrm { f } ( x )\) at \(x = 0.4\).
      (1 mark)

3

1. 1. Express \(3 \cos x + 2 \sin x\) in the form \(R \cos ( x - \alpha )\), where \(R > 0\) and \(0 ^ { \circ } < \alpha < 90 ^ { \circ }\), giving your value of \(\alpha\) to the nearest \(0.1 ^ { \circ }\).
      (3 marks)
   2. Hence find the minimum value of \(3 \cos x + 2 \sin x\) and the value of \(x\) in the interval \(0 ^ { \circ } < x < 360 ^ { \circ }\) where the minimum occurs. Give your value of \(x\) to the nearest \(0.1 ^ { \circ }\).
2. 1. Show that \(\cot x - \sin 2 x = \cot x \cos 2 x\) for \(0 ^ { \circ } < x < 180 ^ { \circ }\).
   2. Hence, or otherwise, solve the equation $$\cot x - \sin 2 x = 0$$ in the interval \(0 ^ { \circ } < x < 180 ^ { \circ }\).

4

1. A curve is defined by the equation \(x ^ { 2 } - y ^ { 2 } = 8\).
   1. Show that at any point \(( p , q )\) on the curve, where \(q \neq 0\), the gradient of the curve is given by \(\frac { \mathrm { d } y } { \mathrm {~d} x } = \frac { p } { q }\).
      (2 marks)
   2. Show that the tangents at the points \(( p , q )\) and \(( p , - q )\) intersect on the \(x\)-axis.
      (4 marks)
2. Show that \(x = t + \frac { 2 } { t } , y = t - \frac { 2 } { t }\) are parametric equations of the curve \(x ^ { 2 } - y ^ { 2 } = 8\).
   (2 marks)

5

1. Find \(\int x \sqrt { x ^ { 2 } + 3 } \mathrm {~d} x\).
   (2 marks)
2. Solve the differential equation $$\frac { \mathrm { d } y } { \mathrm {~d} x } = \frac { x \sqrt { x ^ { 2 } + 3 } } { \mathrm { e } ^ { 2 y } }$$ given that \(y = 0\) when \(x = 1\). Give your answer in the form \(y = \mathrm { f } ( x )\).

6

1. The points \(A , B\) and \(C\) have coordinates \(( 3,1 , - 6 ) , ( 5 , - 2,0 )\) and \(( 8 , - 4 , - 6 )\) respectively.
   1. Show that the vector \(\overrightarrow { A C }\) is given by \(\overrightarrow { A C } = n \left[ \begin{array} { r } 1
      - 1
      0 \end{array} \right]\), where \(n\) is an integer.
   2. Show that the acute angle \(A C B\) is given by \(\cos ^ { - 1 } \left( \frac { 5 \sqrt { 2 } } { 14 } \right)\).
2. Find a vector equation of the line \(A C\).
3. The point \(D\) has coordinates \(( 6 , - 1 , p )\). It is given that the lines \(A C\) and \(B D\) intersect.
   1. Find the value of \(p\).
   2. Show that \(A B C D\) is a rhombus, and state the length of each of its sides.

7 A biologist is investigating the growth of a population of a species of rodent. The biologist proposes the model $$N = \frac { 500 } { 1 + 9 \mathrm { e } ^ { - \frac { t } { 8 } } }$$ for the number of rodents, \(N\), in the population \(t\) weeks after the start of the investigation. Use this model to answer the following questions.

1. 1. Find the size of the population at the start of the investigation.
   2. Find the size of the population 24 weeks after the start of the investigation. your answer to the nearest whole number.
   3. Find the number of weeks that it will take the population to reach 400 . Give your answer in the form \(t = r \ln s\), where \(r\) and \(s\) are integers.
2. 1. Show that the rate of growth, \(\frac { \mathrm { d } N } { \mathrm {~d} t }\), is given by $$\frac { \mathrm { d } N } { \mathrm {~d} t } = \frac { N } { 4000 } ( 500 - N )$$
   2. The maximum rate of growth occurs after \(T\) weeks. Find the value of \(T\).