Mod-Arg Form
y
z =x + iy
y
O
x
x
Modulus
The modulus of a complex number is the
length of the vector OZ
3.
Mod-Arg Form
y
z =x + iy
r z
O
x
Modulus
The modulus of a complex number is the
length of the vector OZ
r 2 x2 y2
r x2 y2
y
x
4.
Mod-Arg Form
y
z =x + iy
r z
O
x
Modulus
The modulus of a complex number is the
length of the vector OZ
r 2 x2 y2
r x2 y2
y
x
z x2 y2
5.
Mod-Arg Form
y
z =x + iy
r z
arg z
O
x
Modulus
The modulus of a complex number is the
length of the vector OZ
r 2 x2 y2
r x2 y2
y
x
z x2 y2
Argument
The argument of a complex number is
the angle the vector OZ makes with the
positive real (x) axis
6.
Mod-Arg Form
y
z =x + iy
r z
arg z
O
x
Modulus
The modulus of a complex number is the
length of the vector OZ
r 2 x2 y2
r x2 y2
y
x
z x2 y2
Argument
The argument of a complex number is
the angle the vector OZ makes with the
positive real (x) axis
y
arg z tan
x
1
arg z
e.g . Findthe modulus and argument of 4 4i
4 4i 4 4
2
32
4 2
2
4
arg4 4i tan
4
tan 1 1
1
4
Every complex number can be written in terms of its modulus and
argument
12.
e.g . Findthe modulus and argument of 4 4i
4 4i 4 4
2
32
4 2
2
4
arg4 4i tan
4
tan 1 1
1
4
Every complex number can be written in terms of its modulus and
argument
z x iy
r cos ir sin
r cos i sin
13.
e.g . Findthe modulus and argument of 4 4i
4 4i 4 4
2
2
32
4 2
4
arg4 4i tan
4
tan 1 1
1
4
Every complex number can be written in terms of its modulus and
argument
z x iy
r cos ir sin
r cos i sin
The mod-arg form of z is;
z r cos i sin
z rcis
where; r z
arg z
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
NOTE:
Multiplication
rotates z1 by
arg z2
26.
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
Proof: let z1 r1cis1 and z 2 r2 cis 2
z1 z 2 r1 cos1 i sin 1 r2 cos 2 i sin 2
NOTE:
Multiplication
rotates z1 by
arg z2
27.
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
Proof: let z1 r1cis1 and z 2 r2 cis 2
NOTE:
Multiplication
rotates z1 by
arg z2
z1 z 2 r1 cos1 i sin 1 r2 cos 2 i sin 2
r1r2 cos1 cos 2 i sin 1 cos 2 i cos1 sin 2 sin 1 sin 2
r1r2 cos1 cos 2 sin 1 sin 2 isin 1 cos 2 cos1 sin 2
28.
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
Proof: let z1 r1cis1 and z 2 r2 cis 2
NOTE:
Multiplication
rotates z1 by
arg z2
z1 z 2 r1 cos1 i sin 1 r2 cos 2 i sin 2
r1r2 cos1 cos 2 i sin 1 cos 2 i cos1 sin 2 sin 1 sin 2
r1r2 cos1 cos 2 sin 1 sin 2 isin 1 cos 2 cos1 sin 2
r1r2 cos1 2 i sin 1 2
29.
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
Proof: let z1 r1cis1 and z 2 r2 cis 2
NOTE:
Multiplication
rotates z1 by
arg z2
z1 z 2 r1 cos1 i sin 1 r2 cos 2 i sin 2
r1r2 cos1 cos 2 i sin 1 cos 2 i cos1 sin 2 sin 1 sin 2
r1r2 cos1 cos 2 sin 1 sin 2 isin 1 cos 2 cos1 sin 2
r1r2 cos1 2 i sin 1 2
z1 z 2 r1r2
z1 z 2
30.
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
Proof: let z1 r1cis1 and z 2 r2 cis 2
NOTE:
Multiplication
rotates z1 by
arg z2
z1 z 2 r1 cos1 i sin 1 r2 cos 2 i sin 2
r1r2 cos1 cos 2 i sin 1 cos 2 i cos1 sin 2 sin 1 sin 2
r1r2 cos1 cos 2 sin 1 sin 2 isin 1 cos 2 cos1 sin 2
r1r2 cos1 2 i sin 1 2
z1 z 2 r1r2
arg z1 z 2 1 2
z1 z 2
arg z1 arg z 2
31.
Mod-Arg Relations
1 z1z2 z1 z2
arg z1 z 2 arg z1 arg z 2
Proof: let z1 r1cis1 and z 2 r2 cis 2
NOTE:
Multiplication
rotates z1 by
arg z2
z1 z 2 r1 cos1 i sin 1 r2 cos 2 i sin 2
r1r2 cos1 cos 2 i sin 1 cos 2 i cos1 sin 2 sin 1 sin 2
r1r2 cos1 cos 2 sin 1 sin 2 isin 1 cos 2 cos1 sin 2
r1r2 cos1 2 i sin 1 2
z1 z 2 r1r2
arg z1 z 2 1 2
z1 z 2
arg z1 arg z 2
NOTE: it follows that;
z1 z 2 z3 z n z1 z 2 z3 z n
arg z1 z 2 z3 z n arg z1 arg z 2 arg z3 arg z n
z1
z1
2
z2z2
z
arg 1 arg z1 arg z 2
z2
NOTE: it follows that;
z1 z 2
z1 z 2
z3 z 4 z3 z 4
z1 z 2
arg
z z arg z1 arg z 2 arg z3 arg z 4
3 4
34.
z1
z1
2
z2z2
z
arg 1 arg z1 arg z 2
z2
NOTE: it follows that;
z1 z 2
z1 z 2
z3 z 4 z3 z 4
z1 z 2
arg
z z arg z1 arg z 2 arg z3 arg z 4
3 4
3 z z
n
n
argz n n arg z
35.
e.g. Find themodulus and argument of z
5 i 2 i
3 2i
36.
e.g. Find themodulus and argument of z
2
2
52 12 2 1
z
32 2 2
5 i 2 i
3 2i
37.
e.g. Find themodulus and argument of z
2
2
52 12 2 1
z
32 2 2
26 5
13
10
5 i 2 i
3 2i
38.
5 i 2 i
e.g. Find the modulus and argument of z
3 2i
2
2
2
2
5 1 2 1
1
2
1
z
2
2
arg z tan 1 tan 1 tan 1
3 2
5
2
3
26 5
13
10
39.
5 i 2 i
e.g. Find the modulus and argument of z
3 2i
2
2
2
2
5 1 2 1
1
2
1
z
2
2
arg z tan 1 tan 1 tan 1
3 2
5
2
3
26 5
1119 153 26 33 41
13
175 48
10
40.
5 i 2 i
e.g. Find the modulus and argument of z
3 2i
2
2
2
2
5 1 2 1
1
2
1
z
2
2
arg z tan 1 tan 1 tan 1
3 2
5
2
3
26 5
1119 153 26 33 41
13
175 48
10
Patel: Exercise 4B; evens
Patel: Exercise 4C; 1 to 10 evens
Cambridge: Exercise 1D; 9, 11, 13, 14, 16, 20