WJEC Further Unit 1 (Further Unit 1) 2022 June

1. The complex numbers \(z , w\) are given by \(z = 3 - 4 \mathrm { i } , w = 2 - \mathrm { i }\).
   1. (i) Find the modulus and argument of \(z w\).
      (ii) Express \(z w\) in the form \(r ( \cos \theta + \mathrm { i } \sin \theta )\).
   2. The complex numbers \(v , w , z\) satisfy the equation \(\frac { 1 } { v } = \frac { 1 } { w } - \frac { 1 } { z }\). Find \(v\) in the form \(a + \mathrm { i } b\), where \(a , b\) are real.
   3. The complex conjugate of \(v\) is denoted by \(\bar { v }\).
   Show that \(v \bar { v } = k\), where \(k\) is a real number whose value is to be determined.

2. (a) The matrices \(\mathbf { A }\) and \(\mathbf { B }\) are defined by $$\mathbf { A } = \left( \begin{array} { c c } 3 & 4
- 1 & - 2 \end{array} \right) , \quad \mathbf { B } = \binom { - 11 } { 7 }$$ Given that \(\mathbf { A X } = \mathbf { B }\), find the matrix \(\mathbf { X }\).
(b) (i) Find the \(2 \times 2\) matrix, \(\mathbf { T }\), which represents a reflection in the line \(y = - 2 x\).
(ii) The images of the points \(C ( 2,7 )\) and \(D ( 3,1 )\), under \(\mathbf { T }\), are \(E\) and \(F\) respectively. Find the coordinates of the midpoint of \(E F\).

3. The vector equation of the line \(L\) is given by $$\mathbf { r } = - \mathbf { i } + 2 \mathbf { j } - 6 \mathbf { k } + \lambda ( 4 \mathbf { i } - 2 \mathbf { j } + 7 \mathbf { k } ) .$$ The Cartesian equation of the plane \(\Pi\) is given by $$3 x + 8 y - 9 z = 0$$ Find the Cartesian coordinates of the point of intersection of \(L\) and \(\Pi\).

4. The positive integer \(N\) is such that \(1 ^ { 2 } + 2 ^ { 2 } + 3 ^ { 2 } + \ldots + N ^ { 2 } = ( 3 N - 2 ) ^ { 2 }\). Write down and simplify an equation satisfied by \(N\). Hence find the possible values of \(N\).

5. (a) The complex number \(z\) is represented by the point \(P ( x , y )\) in an Argand diagram. Given that $$| z - 3 + 2 i | = | z - 3 |$$ find the equation of the locus of \(P\).
(b) Give a geometric interpretation of the locus of \(P\).

6. The roots of the cubic equation $$2 x ^ { 3 } + p x ^ { 2 } - 126 x + q = 0$$ form a geometric progression with common ratio - 3 .
Find the possible values of \(p\) and \(q\), giving your answers in surd form.

7. The vector equations of the lines \(L _ { 1 } , L _ { 2 } , L _ { 3 }\) are given by $$\begin{aligned} & \mathbf { r } = 3 \mathbf { i } + 2 \mathbf { j } + \mathbf { k } + \lambda ( 2 \mathbf { i } + n \mathbf { j } + \mathbf { k } )
& \mathbf { r } = 5 \mathbf { i } - 3 \mathbf { j } - 4 \mathbf { k } + \mu ( 3 \mathbf { i } + \mathbf { j } - 3 \mathbf { k } )
& \mathbf { r } = 6 \mathbf { i } - 3 \mathbf { j } + 2 \mathbf { k } + v ( p \mathbf { i } + 3 \mathbf { j } + 4 \mathbf { k } ) \end{aligned}$$ respectively, where \(n\) and \(p\) are constants.
The line \(L _ { 1 }\) is perpendicular to the line \(L _ { 2 }\). The line \(L _ { 1 }\) is also perpendicular to the line \(L _ { 3 }\).

1. Show that the value of \(n\) is - 3 and find the value of \(p\).
2. Find the acute angle between the lines \(L _ { 2 }\) and \(L _ { 3 }\).

8. The point \(( x , y , z )\) is rotated through \(60 ^ { \circ }\) anticlockwise around the \(z\)-axis. After rotation, the value of the \(x\)-coordinate is equal to the value of the \(y\)-coordinate.
Show that \(y = ( a + \sqrt { b } ) x\), where \(a\), \(b\) are integers whose values are to be determined.

9. (a) Given that \(A _ { r } = \frac { 1 } { r + 1 } - \frac { 2 } { r + 2 } + \frac { 1 } { r + 3 }\), show that \(A _ { r }\) can be expressed as \(\frac { 2 } { ( r + 1 ) ( r + 2 ) ( r + 3 ) }\).
(b) Hence, show that \(\sum _ { r = 1 } ^ { n } \frac { 2 } { ( r + 1 ) ( r + 2 ) ( r + 3 ) } = \frac { 1 } { 6 } - \frac { 1 } { ( n + 2 ) ( n + 3 ) }\).
(c) Find the ratio of \(\sum _ { r = 1 } ^ { 5 } A _ { r } : \sum _ { r = 1 } ^ { 10 } A _ { r }\), giving your answer in its simplest form.