The modulus of a complex number z = a + ib is defined as:
A
√(a² + b²)
B
a + b
C
a - b
D
a² - b²
Analysis & Theory
The modulus of z = a + ib is |z| = √(a² + b²).
If z = 3 + 4i, then |z| equals:
A
5
B
7
C
1
D
25
Analysis & Theory
|z| = √(3² + 4²) = √25 = 5.
If z = -6 + 8i, then |z| equals:
A
10
B
14
C
2
D
1
Analysis & Theory
|z| = √((-6)² + 8²) = √(36 + 64) = √100 = 10.
The modulus of the conjugate of z = a + ib is:
A
|z|
B
-|z|
C
1/|z|
D
|z|²
Analysis & Theory
The modulus of z̅ = a - ib is |z̅| = √(a² + b²) = |z|.
If z₁ = 3 + 4i and z₂ = 1 - 2i, then |z₁z₂| equals:
A
|z₁| × |z₂|
B
|z₁| + |z₂|
C
|z₁| - |z₂|
D
|z₁| / |z₂|
Analysis & Theory
Modulus of a product: |z₁z₂| = |z₁| × |z₂|.
If z₁ = 3 + 4i and z₂ = 1 - 2i, then |z₁ / z₂| equals:
A
|z₁| / |z₂|
B
|z₁| × |z₂|
C
|z₁| + |z₂|
D
|z₁| - |z₂|
Analysis & Theory
Modulus of a quotient: |z₁ / z₂| = |z₁| / |z₂|.
The modulus of a purely imaginary number z = ib is:
A
|b|
B
b
C
0
D
1
Analysis & Theory
For z = ib, |z| = √(0² + b²) = |b|.
The modulus of a purely real number z = a is:
A
|a|
B
a
C
0
D
1
Analysis & Theory
For z = a, |z| = √(a² + 0²) = |a|.
The modulus of z = 1 - i√3 is:
A
2
B
√2
C
1
D
√3
Analysis & Theory
|z| = √(1² + (√3)²) = √(1 + 3) = √4 = 2.
If |z| = 5 and z̅ = a - ib, then a² + b² equals:
A
25
B
5
C
10
D
√5
Analysis & Theory
By definition |z|² = a² + b², so if |z| = 5, then a² + b² = 25.