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Further Pure Mathematics 1

Chapter Assessment
Complex Numbers

1. The complex number α is given by α = –2 + 5j.


(i) Write down the complex conjugate α*.
[1]
(ii) Find the modulus and argument of α.
[3]
  *
(iii) Find in the form a + bj.

[3]

2. (i) Given that w = 1 + 2j, express w², w³ and w4 in the form a + bj.
[5]
(ii) Given that w is a root of the equation z  pz  qz  6 z  65  0 , find the
4 3 2

values of p and q.
[5]
(iii) Write down a second root of the equation.
[1]
(iv) Find the other two roots of the equation.
[6]

3. (i) Show that z1 = 2 + j is one of the roots of the equation z² – 4z + 5 = 0.


Find the other root, z2.
[3]
1 1 4
(ii) Show that   .
z1 z2 5
[3]
(iii) Show also that Im (z1² + z2²) = 0 and find Re (z1² – z2²).
[4]
(iv) Find in the form r (cos   jsin  ) , the complex numbers z1, z1², and z1³.
[7]
(v) Plot the three complex numbers z1, z1², and z1³ on an Argand diagram.
[3]

© MEI, September 2001


Further Pure Mathematics 1

4. (a) Solve the equation z² + 2z + 10 = 0.


Find the modulus and argument of each root.
[4]
(b) Complex numbers α and β are given by
    5 5 
  2  cos  jsin  ,   4 2  cos  jsin 
 8 8  8 8 
(i) Write down the modulus and argument of each of the complex
numbers α and β.
Illustrate these two complex numbers on an Argand diagram.
[3]
(ii) Indicate a length on your diagram which is equal to    , and show
that     6 .
[3]
(iii) On your diagram, draw and label
(A) the locus L of points representing complex numbers z such that
z   6 ,
[3]
(B) the locus M of points representing complex numbers z such that
5
arg( z   )  .
8
[3]

© MEI, September 2001

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