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Complex Numbers 2 The Argand Diagram Representing Complex Numbers Real numbers are usually represented as positions on a horizontal number line. Real -3 -2 -1 0 1 2 3 4 5 Addition, subtraction, multiplication and division with real numbers takes place on this number line. The Argand Diagram Complex numbers also have an imaginary part so another dimension needs to be added to the number line Imaginary 7 6 5 4 3 2 1 -8 -7 -6 -5 -4 -3 -2 -1 -2 -3 -4 -5 -6 -7 Real 1 2 3 4 5 6 7 8 Complex numbers can be represented on the Argand diagram by straight lines. Putting complex numbers on an Argand diagram often helps give a feel for a problem. Some examples u 62j v 27j w 5 4 j z 7 6 j Imaginary 7 6 5 4 w 3 u 2 1 Real -8 -7 -6 -5 -4 -3 -2 -1 1 2 -2 -3 -4 -5 z -6 -7 v 3 4 5 6 7 8 Complex numbers and their conjugates Imaginary w 5 4 j w* 5 4 j z 6 3 j z* 6 3 j 7 6 5 w 4 z* 3 2 1 Real -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 -2 z -3 -4 -5 -6 -7 w* 6 7 8 Addition Imaginary w 54j 7 6 w 5 4 3 z 6 3 j 2 1 Real z -8 -7 -6 -5 -4 -3 -2 -1 -2 -3 w z -4 -5 -6 -7 1 2 3 4 5 6 7 8 Subtraction Imaginary u 23j 7 v 63j 6 5 4 u v 3 2 1 Real -8 -7 -6 -5 -4 -3 -2 -1 -2 -3 -4 -5 -6 -7 1 2 3 4 5 6 7 8 The modulus of a complex number Imaginary x yj x y 2 x + yj y Real O x 2 The argument of a complex number Imaginary z 23j w 3 5 j 7 6 5 4 z=2 + 3j 3 between -180o and 180o 2 1 -8 -7 -6 -5 -4 -3 -2 -1 1 -2 α -3 -4 -5 w=-3 - 5j θ -6 -7 Real 2 3 4 5 6 7 8 arg( z ) arctan( 32 ) 56 arctan( 53 ) 59 arg( w) 121 Radians 180 c 180 c 60 3 3 c 5 180 5 150 6 6 Loci using complex numbers z 64j zw w 1 2 j 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 The distance to a point z (3 2 j ) z (4 7 j ) z 47j Imaginary z (3 2 j) 4 7 6 5 4 3 2 z (3 2 j) 4 1 Real -8 -7 -6 -5 -4 -3 -2 -1 z (3 2 j) 4 -2 z (3 2 j) 4 -5 -3 -4 -6 -7 1 2 3 4 5 4 6 7 8 Loci using arguments arg( z ) Im arg( z j ) 4 Re 0 arg( z j ) Im 4 Re Im 4 Re