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# Complex Numbers

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### Complex Numbers

1. 1. COMPLEX NUMBERS
2. 2. THE COMPLEX NUMBER SYSTEMThere is no real number x which satisfies the polynomialequation x2 + 1 = 0. To permit solutions of this and similarequations, the set of complex numbers is introduced.We can consider a complex number as having the forma + i b where a and b are real number and i, which is calledthe imaginary unit, has the property that i2 = – 1.It is denoted by z i.e. z = a + ib. ‘a’ is called as real part of zwhich is denoted by (Re z) and ‘b’ is called as imaginarypart of z which is denoted by (Im z).Any complex number is :i. Purely real, if b = 0 ;ii. Purely imaginary, if a = 0iii. Imaginary, if b ≠ 0.
3. 3. NOTE
4. 4. EXAMPLES
5. 5. ALGEBRAIC OPERATIONS
6. 6. Inequalities in complex numbers are not defined. There isno validity if we say that complex number is positive ornegative.e.g. z > 0, 4 + 2i < 2 + 4i are meaningless.In real numbers if a2 + b2 = 0 then a = 0 = b however incomplex numbers, z12 + z22 = 0 does not imply z1 = z2 = 0.Example : Simplify in+100 + in+50 + in+48 + in+46 , n Î I. Ans. 0
7. 7. EQUALITY IN COMPLEX NUMBER
8. 8. REPRESENTATION OF A COMPLEX NUMBER
9. 9. Note : Argument of a complex number is a many valued function. If q is the argument of a complex number then 2n + ; n I will also be the argument of that complex number. Any two arguments of a complex number differ by 2n . The unique value of such that - < is called the principal value of the argument. Unless otherwise stated, amp z implies principal value of the argument. By specifying the modulus & argument a complex number is defined completely. For the complex number 0 + i0 the argument is not defined and this is the only complex number which is only given by its modulus.
10. 10.
11. 11. EXAMPLES
12. 12. MODULUS OF A COMPLEX NUMBER
13. 13. EXAMPLES|z – 3| < 1 and |z – 4i| > M then find the positive real valueof M for which these exist at least one complex number zsatisfy both the equation. Ans. M (0, 6)
14. 14. ARGUMENT OF A COMPLEX NUMBER
15. 15. PROPERTIES OF ARGUMENTS arg (z1z2) = arg(z1) + arg(z2) + 2m for some integer m. arg (z1/z2) = arg (z1) – arg(z2) + 2m for some integer m. arg (z2) = 2arg(z) + 2m for some integer m. arg (z) = 0 z is real, for any complex number z ≠ 0 arg (z) = ± /2 z is purely imaginary, for any complex number z ≠ 0 arg (z2 – z1) = angle of the line segmentP Q || PQ , where P lies on real axis, with the real axis.
16. 16. EXAMPLES
17. 17. CONJUGATE OF A COMPLEX NUMBER
18. 18. PROPERTIES OF CONJUGATE
19. 19. EXAMPLES
20. 20. ROTATION THEOREM
21. 21. EXAMPLES z1, z2, z3, z4 are the vertices of a square taken in anticlockwise order then prove that 2z2 = (1 + i) z1 + (1 – i) z3 Check that z1z2 and z3z4 are parallel or, not where, z1 = 1 + i z3 = 4 + 2i z2 = 2 – i z4 = 1 – i Ans. Hence, z1z2 and z3z4 are not parallel.
22. 22. DEMOIVRE’S THEOREMCase IStatement :If n is any integer thena) (cos θ + i sin θ )n = cos nθ + i sin nθb) (cos θ1 + i sin θ1) (cos θ2 + i sin θ2) (cos θ3 + i sin θ2)....... ……….(cos θn + i sin θn) = cos (θ1 + θ2 + θ3 + ......... θn) + i sin(θ1 + θ2 + θ3 +.......+ θn)
23. 23.
24. 24. CUBE ROOT OF UNITY
25. 25. EXAMPLES
26. 26. NTH ROOTS OF UNITYIf 1, 1, 2, 3..... n-1 are the n, nth root of unity then :I. They are in G.P. with common ratio ei(2 /n)II. 1p + 1 p+ 2 p +.... + n p = 0 if p is not an integral multiple of n = n if p is an integral multiple of nIII. (1 – 1) (1 – 2)...... (1 – n-1) =n (1 + 1) (1 + 2)....... (1 + n-1) = 0 if n is even and =1 if n is odd.IV. 1. 1. 2 . 3......... n-1 = 1 or –1 according as n is odd or even.
27. 27. EXAMPLES
28. 28. THE SUM OF THE FOLLOWING SERIES SHOULDBE REMEMBERED
29. 29. LOGARITHM OF A COMPLEX QUANTITY
30. 30. EXAMPLES
31. 31. GEOMETRICAL PROPERTIES
32. 32. If a, b, c are three real numbers such thataz1 + bz2 + cz3 = 0 ; where a + b + c = 0 and a,b,c are notall simultaneously zero, then the complex numbersz1, z2 & z3 are collinear.
33. 33.
34. 34. 1. amp(z) = θ is a ray emanating from the origin inclined at an angle θ to the x- axis.2. |z – a| = |z – b| is the perpendicular bisector of the line joining a to b.3. The equation of a line joining z1 & z2 is given by z= z1 + t (z1 – z2) where t is a real parameter.4. z = z1 (1 + it) where t is a real parameter is a line through the point z1 & perpendicular to the line joining z1 to the origin.
35. 35.
36. 36.
37. 37.
38. 38.  z1 z1 1 1 z2 z2 1 4i z3 z3 1 | z0 z0 r| 2| |
39. 39.
40. 40.
41. 41. REFLECTION POINTS FOR A STRAIGHT LINE
42. 42. INVERSE POINTS W.R.T. A CIRCLE
43. 43. PTOLEMY’S THEOREMIt states that the product of the lengths of the diagonals of aconvex quadrilateral inscribed in a circle is equal to the sumof the products of lengths of the two pairs of its oppositesides. i.e. |z1 – z3||z2 – z4|=|z1 – z2||z3 – z4|+|z1 – z4||z2 – z3|