CAIE
FP1
2010
June
Q8
9 marks
Challenging +1.2
8 Obtain the general solution of the differential equation
$$\frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } + 5 \frac { \mathrm {~d} y } { \mathrm {~d} x } + 4 y = 10 \sin 3 x - 20 \cos 3 x$$
Show that, for large positive \(x\) and independently of the initial conditions,
$$y \approx R \sin ( 3 x + \phi )$$
where the constants \(R\) and \(\phi\), such that \(R > 0\) and \(0 < \phi < 2 \pi\), are to be determined correct to 2 decimal places.
CAIE
FP1
2011
June
Q2
6 marks
Standard +0.8
2 The roots of the equation
$$x ^ { 3 } + p x ^ { 2 } + q x + r = 0$$
are \(\frac { \beta } { k } , \beta , k \beta\), where \(p , q , r , k\) and \(\beta\) are non-zero real constants. Show that \(\beta = - \frac { q } { p }\).
Deduce that \(r p ^ { 3 } = q ^ { 3 }\).
CAIE
FP1
2011
June
Q10
12 marks
Challenging +1.2
10 Let
$$I _ { n } = \int _ { 0 } ^ { \frac { 1 } { 2 } \pi } \cos ^ { n } x \mathrm {~d} x$$
where \(n \geqslant 0\). Show that, for all \(n \geqslant 2\),
$$I _ { n } = \frac { n - 1 } { n } I _ { n - 2 }$$
A curve has parametric equations \(x = a \sin ^ { 3 } t\) and \(y = a \cos ^ { 3 } t\), where \(a\) is a constant and \(0 \leqslant t \leqslant \frac { 1 } { 2 } \pi\). Show that the mean value \(m\) of \(y\) over the interval \(0 \leqslant x \leqslant a\) is given by
$$m = 3 a \int _ { 0 } ^ { \frac { 1 } { 2 } \pi } \left( \cos ^ { 4 } t - \cos ^ { 6 } t \right) \mathrm { d } t$$
Find the exact value of \(m\), in terms of \(a\).
CAIE
FP1
2011
June
Q11 EITHER
Challenging +1.3
Use de Moivre's theorem to prove that
$$\tan 3 \theta = \frac { 3 \tan \theta - \tan ^ { 3 } \theta } { 1 - 3 \tan ^ { 2 } \theta }$$
State the exact values of \(\theta\), between 0 and \(\pi\), that satisfy \(\tan 3 \theta = 1\).
Express each root of the equation \(t ^ { 3 } - 3 t ^ { 2 } - 3 t + 1 = 0\) in the form \(\tan ( k \pi )\), where \(k\) is a positive rational number.
For each of these values of \(k\), find the exact value of \(\tan ( k \pi )\).
CAIE
FP1
2011
June
Q3
6 marks
Standard +0.3
3 Find a cubic equation with roots \(\alpha , \beta\) and \(\gamma\), given that
$$\alpha + \beta + \gamma = - 6 , \quad \alpha ^ { 2 } + \beta ^ { 2 } + \gamma ^ { 2 } = 38 , \quad \alpha \beta \gamma = 30 .$$
Hence find the numerical values of the roots.
CAIE
FP1
2011
June
Q4
8 marks
Standard +0.8
4 The curve \(C\) has equation
$$2 x y ^ { 2 } + 3 x ^ { 2 } y = 1$$
Show that, at the point \(A ( - 1,1 )\) on \(C , \frac { \mathrm {~d} y } { \mathrm {~d} x } = - 4\).
Find the value of \(\frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } }\) at \(A\).