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\today 
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\begin{document}
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\section*{Section A: \ \ \ Pure Mathematics}

%%%%%%%%%%Q1
\begin{question}
\begin{questionparts} \item Guess an expression for 
\[
\left(1-\frac{1}{4}\right)\left(1-\frac{1}{9}\right)\cdots\left(1-\frac{1}{n^{2}}\right),
\]
valud for $n\geqslant2,$ and prove by mathematical induction the
correctness of your guess. 


\item Show that, if $n$ is a positive integer, 
\[
\sum_{r=0}^{k}(-1)^{r}\binom{n}{r}=(-1)^{k}\binom{n-1}{k},\qquad\mbox{ for }k=0,1,\ldots,n-1.
\]
\end{questionparts}
\end{question}

%%%%%%%%%%Q2
\begin{question}
Show by using the binomial expansion, or otherwise, that $(1+x)^{n}>nx$
whenever $x\geqslant0$ and $n$ is a positive integer. Deduce that
if $y>1$ then, given any number $K$, an integer $N$ can be found
such that $y^{n}>K$ for all integers $n\geqslant N.$ 


Show further that if $y>1$ then, given any $K$, an integer $N$
can be found such that $\dfrac{y^{n}}{n}>K$ for all integers $n\geqslant N$. 

\end{question}

%%%%%%%%% Q3
\begin{question}
For the complex numbers $z_{1}$ and $z_{2}$ interpret geometrically
the inequality 
\[
\left|z_{1}+z_{2}\right|\leqslant\left|z_{1}\right|+\left|z_{2}\right|.
\]
Prove that, if $\left|a_{i}\right|\leqslant2$ for $i=1,2,\ldots,n,$
then the equation 
\[
a_{1}z+a_{2}z^{2}+\cdots+a_{n}z^{n}=1
\]
has no solutions with $\left|z\right|\leqslant\frac{1}{3}.$ 
\end{question}


%%%%%% Q4 

\begin{question}
	Prove that the straight line 
\[
ty=x+at^{2}
\]
touches the parabola $y^{2}=4ax$ and find the coordinates of the
point of contact. 


The tangents from a point to the parabola meet the directrix $(x=-a)$
in points $L$ and $M$. Show that, if $LM$ is of a fixed length
$\ell,$ the point must lie on 
\[
(x+a)^{2}(y^{2}-4ax)=\ell^{2}x^{2}.
\]
\end{question}


%%%%%%%%% Q5
\begin{question}
The equation 
\[
\sin x=\lambda x,\qquad x\geqslant0,
\]
where $\lambda>0,$ has a finite number $N$ of non-zero solutions
$x_{n},$ $i=1,\ldots,N,$ where $N$ depends on $\lambda,$ provided
$\lambda<1$. 

\begin{questionparts}
\item Show by a graphical argument that there are no non-zero solutions
for $\lambda>1.$ Show also that for $\lambda=1-\epsilon^{2},$ with
$\epsilon>0$ and very small compared to 1, there is a non-zero solution
approximately equal to $\epsilon\sqrt{6}.$ 
\item Suppose that $N=2R+1$ where $R$ is an integer, and that $x_{1}<x_{2}<\cdots<x_{2R+1}.$
By drawing an appropriate graph, explain why 
\begin{alignat*}{3}
(2n-2)\pi & <x_{2n-1} &  & <(2n-1)\pi & \quad & \mbox{ for }n=1,\ldots,R+1,\\
2n\pi & <x_{2n} &  & <(2n+\tfrac{1}{2})\pi & \quad & \mbox{ for }n=1,\ldots,R.
\end{alignat*}
Hence derive an approximate value for $N$ in terms of $\lambda,$
when $\lambda$ is very small. 
\end{questionparts}
	 \end{question}
	 
	 %%%%%%%%% Q6
\begin{question}
Let 
\[
I_{n}=\int_{0}^{\infty}\mathrm{sech}^{n}u\,\mathrm{d}u.
\]
Show that for $n>0$ 
\[
\int_{0}^{\infty}\mathrm{sech}^{n+2}u\,\sinh^{2}u\,\mathrm{d}u=\frac{1}{n+1}I_{n},
\]
and deduce that 
\[
(n+1)I_{n+2}=nI_{n}.
\]
Find the value of $I_{6}.$ 
	\end{question}
	
	%%%%%%%%% Q7
	\begin{question}
Show that the differential equation 
\[
x^{2}y''+(x-2)(xy'-y)=0
\]
has a solution proportional to $x^{\alpha}$ for some $\alpha.$ By
making the substitution $y=x^{\alpha}v$, or otherwise, find the general
solution of this equation. 
		
		\end{question}
		
		
%%%%%%%%% Q8
		\begin{question}
\begin{questionparts}
	\item Using vectors, or otherwise, prove that the
sum of the squares of the edges of any tetrahedron equals four times
the sum of the squares of the lines joining the midpoints of opposite
edges. 


\item By using the inequality 
\[
\left|\mathbf{a}\cdot\mathbf{b}\right|\leqslant\left|\mathbf{a}\right|\left|\mathbf{b}\right|
\]
with a suitable choices of three-dimensional vectors $\mathbf{a}$
and $\mathbf{b}$, or otherwise, prove that 
\[
3x+2y+6\leqslant7\sqrt{x^{2}+y^{2}+1}.
\]
For what values of $x$ and $y$ does the equality sign hold? 
\end{questionparts}
		\end{question}
		
	
%%%%%%%%%% 9
\begin{question}
Prove that the set of all matrices of the form 
\[
\begin{pmatrix}1 & 0 & 0\\
x & 1 & 0\\
y & z & 1
\end{pmatrix},
\]
where $x,y$ and $z$ are real numbers, is a group $G$ under matrix
multiplication. (You may assume that matrix multiplication is associative.)


Does the subset consisting of these matrices where $x,y,z$ are restricted
to the integers form a subgroup of $G$? Is there an element $\mathbf{A}$
in $G$, with $\mathbf{A}$ not equal to the identity matrix, such
that $\mathbf{AB=BA}$ for all $\mathbf{B}$ belonging to $G$? Justify
your answer. 
\end{question}
%%%%%%%%%% 10
\begin{question}
\begin{questionparts}
	\item Show that every odd square leaves remainder
	1 when divided by 8, and that every even square leaves remainder 0
	or 4. Deduce that a number of the form $8n+7,$ where $n$ is a positive
	integer, cannot be expressed as a sum of three squares. 


	\item Prove that 17 divides $2^{3n+1}+3(5^{2n+1})$ for all integers
	$n\geqslant0.$ \end{questionparts}
\end{question}

			
		
		
		
	
\newpage
\section*{Section B: \ \ \ Mechanics}


	
%%%%%%%%%% Q11
\begin{question}
Two identical snowploughs plough the same stretch of road in the same
direction. The first starts at time $t=0$ when the depth of snow
is $h$ metres, and the second starts from the same point $T$ seconds
later. Snow falls so that the depth of snow increases at a constant
rate of $k$ ms$^{-1}$. It may be assumed that each snowplough moves
at a speed equal to $k/(\alpha z)$ ms$^{-1}$ with $\alpha$ a constant,
where $z$ is the depth of snow it is ploughing, and that it clears
all the snow. 

\begin{questionparts}
\item Show that the time taken for the first snowplough to travel $x$ metres
is 
\[
(\mathrm{e}^{\alpha x}-1)\frac{h}{k}\ \mbox{ seconds}.
\]

\item Show that at time $t>T,$ the second snowplough has moved $y$ metres,
where $t$ satisfies 
\[
\frac{1}{\alpha}\frac{\mathrm{d}t}{\mathrm{d}y}=t-\left(\mathrm{e}^{\alpha y}-1\right)\frac{h}{k}.
\]
Verify that the required solution of this equation is 
\[
t=\left(\mathrm{e}^{\alpha y}-1\right)\frac{h}{k}+\left(T-\frac{\alpha hy}{k}\right)\mathrm{e}^{\alpha y}
\]
and deduce that the snowploughs collide when they have moved a distance
$kT/(\alpha h)$ metres. 
\end{questionparts}

	\end{question}
	
%%%%%%%%%% Q12
\begin{question}	
One end $A$ of a uniform straight rod $AB$ of mass $M$ and length
$L$ rests against a smooth vertical wall. The other end $B$ is attached
to a light inextensible string $BC$ of length $\alpha L$ which is
fixed to the wall at a point $C$ vertically above $A$. The rod is
in equilibrium with the points $A,B$ and $C$ not collinear. Determine
the inclination of the rod to the vertical and the set of possible
values of $\alpha.$ 


Show that the tension in the string is 
\[
\frac{Mg\alpha}{2}\left(\frac{3}{\alpha^{2}-1}\right)^{\frac{1}{2}}.
\]
\end{question}

%%%%%%%%%% Q13

\begin{question}
A particle of mass $m$ is attached to a light circular hoop of radius
$a$ which is free to roll in a vertical plane on a rough horizontal
table. Initially the hoop stands with the particle at its highest
point and is then displaced slightly. Show that while the hoop is
rolling on the table, the speed $v$ of the particle when the radius
to the particle makes an angle $2\theta$ with the upward vertical
is given by 
\[
v=2(ga)^{\frac{1}{2}}\sin\theta.
\]
Write down expressions in terms of $\theta$ for $x$, the horizontal
displacement of the particle from its initial position, and $y$,
its height above the table, and use them to show that 
\[
\theta=\tfrac{1}{2}(g/a)^{\frac{1}{2}}\tan\theta
\]
and 
\[
\ddot{y}=-2g\sin^{2}\theta.
\]



By considering the reaction of the table on the hoop, or otherwise,
describe what happens to prevent the hoop rolling beyond the position
for which $\theta=\pi/4.$ 
\end{question}
	
%%%%%%%%%% Q14
\begin{question}
A uniform straight rod of mass $m$ and length $4a$ can rotate freely
about its midpoint on a smooth horizontal table. Initially the rod
is at rest. A particle of mass $m$ travelling on the table with speed
$u$ at right angles to the rod collides perfectly elastically with
the rod at a distance $a$ from the centre of the rod. Show that the
angular speed, $\omega,$ of the rod after the collision is given
by 
\[
a\omega=6u/7.
\]
Show also that the particle and rod undergo a subsequent collision.
\end{question}
	
	\newpage
\section*{Section C: \ \ \ Probability and Statistics}


%%%%%%%%%% Q15
\begin{question}
The mountain villages $A,B,C$ and $D$ lie at the vertices of a tetrahedron,
and each pair of villages is joined by a road. After a snowfall the
probability that any road is blocked is $p$, and is independent of
the conditions on any other road. Find the probability that it is
possible to travel from any village to any other village by some route
after a snowfall. In the case $p=\frac{1}{2}$ show that this probability
is $19/32.$ 
\end{question}

%%%%%%%%%% Q16
\begin{question}
	The new president of the republic has no children. According to custom,
	he decides on accession that he will have no more children once he
	has $r$ sons. It may be assumed that each baby born to him is equally
	likely to be a boy or a girl, irrespective of the sexes of his previous
	children. Let $C$ be the final number of children in his family.
\begin{questionparts}

\item Find, in terms of $r$, the expectation of $C.$
\item By considering the numbers of boys and girls among $2r-1$ children,
or otherwise, show that $\mathrm{P}(C<2r)=\frac{1}{2}.$ 
 \end{questionparts}
\end{question}
\end{document}
