A circular disc of radius \(r\) is thrown at random onto a large board divided into squares of side \(a\) (where \(a > 2r\)). Show that the probability that the disc comes to rest entirely within one square is \(\left(1 - \frac{2r}{a}\right)^2\). If, instead of a disc, a thin pencil of length \(l\) (where \(l \leq a\)) is thrown on to the board, show that the probability that the pencil does not come to rest entirely within one square is \(\frac{(4a-l)l}{\pi a^2}\).
If \(x_0\) and \(x_1\) are two given positive real numbers and \(x_2, x_3, \ldots\) are determined successively by the formula $$x_n = \sqrt{(x_{n-1} \cdot x_{n-2})} \quad (n = 2, 3, \ldots),$$ show that \(x_n \rightarrow x_0^{1/3} x_1^{2/3}\) as \(n \rightarrow \infty\).
Either by showing that \(n!e\) is never an integer (for \(n = 1, 2, \ldots\)), or in any way, prove that $$e = 1 + \frac{1}{1!} + \frac{1}{2!} + \cdots$$ is irrational (that is, it cannot be expressed in the form \(p/q\) with \(p\) and \(q\) integral).
By using the identity $$\frac{1}{y+1} = \frac{1}{y-1} - \frac{2}{y^2-1},$$ or otherwise, determine for what real values of \(x\) the series $$\sum_{n=1}^{\infty} \frac{2n}{x^{2n} + 1}$$ is convergent and show that when it is convergent the series has sum \(\frac{2}{x^2-1}\).
Show that for each integer \(n \geq 1\) there is a polynomial \(T_n(x)\) of degree \(n\) such that $$T_n(\cos t) = \cos nt$$ for all real \(t\). Show furthermore that, for each such integer \(n\), \(|T_n(x)| \leq 1\) if \(-1 \leq x \leq 1\) but \(|T_n(x)| > 1\) for all real \(x\) outside this range.
Show that the function $$f(x) = \int_x^{2x} \frac{\sin t}{t} dt$$ is bounded for \(x > 0\), and find the points \(x\) at which it attains its greatest and least values in this range. (A function \(f(x)\) is said to be bounded over a certain range if a real number \(C\) can be found such that \(|f(x)| \leq C\) for all \(x\) in that range.)
If \(\Gamma\) is a circle with centre \(C\), and \(A, B\) are two points in the same plane as \(\Gamma\) (but not on \(\Gamma\)), show that \(AX + BX\) attains its minimum as \(X\) varies on \(\Gamma\) at a point at which \(AX\) and \(BX\) are equally inclined to \(CX\). Hence or otherwise show that if \(A, B, C\) are three fixed points and \(P\) is a point (in the plane of \(A, B\) and \(C\)) at which \(AP + BP + CP\) is a minimum, then either \(P\) is one of the points \(A, B\), or \(C\), or else $$\widehat{BPC} = \widehat{CPA} = \widehat{APB} = \frac{2\pi}{3}.$$