Edexcel P4 (Pure Mathematics 4) 2023 October

1. (a) Find the first four terms, in ascending powers of \(x\), of the binomial expansion of

$$\frac { 8 } { ( 2 - 5 x ) ^ { 2 } }$$ writing each term in simplest form.
(b) Find the range of values of \(x\) for which this expansion is valid.

2. \begin{figure}[h] \end{figure} Figure 1 shows a cube which is increasing in size.
At time \(t\) seconds,

• the length of each edge of the cube is \(x \mathrm {~cm}\)
• the surface area of the cube is \(S \mathrm {~cm} ^ { 2 }\)
• the volume of the cube is \(V \mathrm {~cm} ^ { 3 }\)

Given that the surface area of the cube is increasing at a constant rate of \(4 \mathrm {~cm} ^ { 2 } \mathrm {~s} ^ { - 1 }\)

1. show that \(\frac { \mathrm { d } x } { \mathrm {~d} t } = \frac { k } { x }\) where \(k\) is a constant to be found,
2. show that \(\frac { \mathrm { d } V } { \mathrm {~d} t } = V ^ { p }\) where \(p\) is a constant to be found.

1. In this question you must show all stages of your working.

\section*{Solutions based on calculator technology are not acceptable.}

1. Use integration by parts to find the exact value of $$\int _ { 0 } ^ { 4 } x ^ { 2 } \mathrm { e } ^ { 2 x } \mathrm {~d} x$$ giving your answer in simplest form.
2. Use integration by substitution to show that $$\int _ { 3 } ^ { \frac { 21 } { 2 } } \frac { 4 x } { ( 2 x - 1 ) ^ { 2 } } \mathrm {~d} x = a + \ln b$$ where \(a\) and \(b\) are constants to be found.

1. (a) Prove by contradiction that for all positive numbers \(k\)

$$k + \frac { 9 } { k } \geqslant 6$$ (b) Show that the result in part (a) is not true for all real numbers.

5. \begin{figure}[h] \end{figure} Figure 2 shows a sketch of the curve \(C\) with equation $$y ^ { 3 } - x ^ { 2 } + 4 x ^ { 2 } y = k$$ where \(k\) is a positive constant greater than 1

1. Find \(\frac { \mathrm { d } y } { \mathrm {~d} x }\) in terms of \(x\) and \(y\). The point \(P\) lies on \(C\).
   Given that the normal to \(C\) at \(P\) has equation \(y = x\), as shown in Figure 2,
2. find the value of \(k\).

1. The line \(l _ { 1 }\) has equation \(\mathbf { r } = \left( \begin{array} { r } 2
   3
   - 7 \end{array} \right) + \lambda \left( \begin{array} { l } 1
   2
   2 \end{array} \right)\) where \(\lambda\) is a scalar parameter.

The line \(l _ { 2 }\) has equation \(\mathbf { r } = \left( \begin{array} { r } 2
3
- 7 \end{array} \right) + \mu \left( \begin{array} { r } 4
- 1
8 \end{array} \right)\) where \(\mu\) is a scalar parameter.
Given that \(l _ { 1 }\) and \(l _ { 2 }\) meet at the point \(P\)

1. state the coordinates of \(P\) Given that the angle between lines \(l _ { 1 }\) and \(l _ { 2 }\) is \(\theta\)
2. find the value of \(\cos \theta\), giving the answer as a fully simplified fraction. The point \(Q\) lies on \(l _ { 1 }\) where \(\lambda = 6\)
   Given that point \(R\) lies on \(l _ { 2 }\) such that triangle \(Q P R\) is an isosceles triangle with \(P Q = P R\)
3. find the exact area of triangle \(Q P R\)
4. find the coordinates of the possible positions of point \(R\)

1. The number of goats on an island is being monitored.

When monitoring began there were 3000 goats on the island.
In a simple model, the number of goats, \(x\), in thousands, is modelled by the equation $$x = \frac { k ( 9 t + 5 ) } { 4 t + 3 }$$ where \(k\) is a constant and \(t\) is the number of years after monitoring began.

1. Show that \(k = 1.8\)
2. Hence calculate the long-term population of goats predicted by this model. In a second model, the number of goats, \(x\), in thousands, is modelled by the differential equation $$3 \frac { \mathrm {~d} x } { \mathrm {~d} t } = x ( 9 - 2 x )$$
3. Write \(\frac { 3 } { x ( 9 - 2 x ) }\) in partial fraction form.
4. Solve the differential equation with the initial condition to show that $$x = \frac { 9 } { 2 + \mathrm { e } ^ { - 3 t } }$$
5. Find the long-term population of goats predicted by this second model.

8. \begin{figure}[h] \end{figure} Figure 3 shows a sketch of the curve \(C\) with parametric equations $$x = 6 t - 3 \sin 2 t \quad y = 2 \cos t \quad 0 \leqslant t \leqslant \frac { \pi } { 2 }$$ The curve meets the \(y\)-axis at 2 and the \(x\)-axis at \(k\), where \(k\) is a constant.

1. State the value of \(k\).
2. Use parametric differentiation to show that $$\frac { \mathrm { d } y } { \mathrm {~d} x } = \lambda \operatorname { cosec } t$$ where \(\lambda\) is a constant to be found. The point \(P\) with parameter \(\mathrm { t } = \frac { \pi } { 4 }\) lies on \(C\).
   The tangent to \(C\) at the point \(P\) cuts the \(y\)-axis at the point \(N\).
3. Find the exact \(y\) coordinate of \(N\), giving your answer in simplest form. The region bounded by the curve, the \(x\)-axis and the \(y\)-axis is rotated through \(2 \pi\) radians about the \(x\)-axis to form a solid of revolution.
4. 1. Show that the volume of this solid is given by $$\int _ { 0 } ^ { \alpha } \beta ( 1 - \cos 4 t ) d t$$ where \(\alpha\) and \(\beta\) are constants to be found.
   2. Hence, using algebraic integration, find the exact volume of this solid.