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Last updated on August 26th, 2025

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Modulus of Complex Number

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The square root of the sum of squares for the real and imaginary parts of a complex number is its modulus. The modulus of a complex number tells you how far it is from the origin on the complex plane. It’s always a non-negative value.

Modulus of Complex Number for Filipino Students
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What is a Complex Number?

A complex number in mathematics is an expression of the form a+bi, where i is the imaginary unit (√-1) and a and b are real numbers.
 

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What is the Modulus of a Complex Number?

The square root of the sum of the squares of the complex number’s real and imaginary parts is its modulus. |z| or r Represents the modulus of a complex number z=x+iy, which is defined as follows:
|z|=x2+y2.
 

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What is the Conjugate of a Complex Number?

In mathematics, a complex number’s conjugate is created by inverting the sign of its imaginary component while leaving the real component unaltered. When a complex number z=a+bi is given, with ‘a’ standing for the real component and ‘b’ for the imaginary component, and ‘i’ for the imaginary component, and ‘i’ for the imaginary unit (√-1), its conjugate, z is defined as a-bi.
For example,
If z=5+3i,
Then its conjugate is z = 5-3i
 

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How to Find the Conjugate of a Complex Number?

Simply changing the sign of the imaginary part of a complex number while maintaining the same sign for the real part gives the conjugate.
Formula:
Complex number is written as,
z=a+bi
Conjugate is,
z = a-bi
For example,
z=6+2i
Now, change the sign of the imaginary part of a complex number.
Conjugate,
z = 6-2i
 

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Modulus of Complex Number Using Graph

The distance between the complex number’s coordinates and the center of the complex plane is said to be the modulus of the complex number when it is shown on a graph. A complex number’s modulus is the distance between two complex numbers. It is presented as a point on the Argand plane (a, b). This distance is measured as r=(a2+b2) and is a linear distance from the center (0, 0) to the point (a, b). Moreover, the Pythagoras theorem can be used to determine the modulus of a complex number. Here, the hypotenuse represents the modulus, the real component is the base, and the imaginary part seems to be the perpendicular of the right-angled triangles.  
     r=a2+b2
 

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Properties of Modulus of Complex Number

Some of the properties of a complex number are listed below. Given two complex numbers, z and w, we have:

  • Complex numbers z and -z have the same modulus, so |z|=|-z|.
  • A complex number’s modulus is zero only if it is zero; that is, |z|=0 if z=0.
  • The modulus of a product equals the product of moduli: zw = zw
     
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Real-World Applications of Modulus of Complex Number

The modulus of a complex number is used in real-world applications. Let us see how it is used.

 


Ac circuits in electrical engineering
The magnitude of impedance, or how much a circuit resists the flow of alternating current, is found using the modulus of a complex number in AC circuit analysis.

 


Processing of signals
When signals are expressed as complex numbers in the frequency domain (such as in Fourier transforms), the modulus indicates the strength of each frequency, or, to put it another way, the strength of the signal at that frequency.

 


Systems of control
Engineers use the modulus to examine the distances between specific points (referred to as poles and zeros) and the complex plane’s center. They can determine whether the system will behave steadily or become unstable.

 


Wave machines in physics
The probability amplitude or wave intensity is represented by the modulus of a complex number in quantum mechanics and wave physics.

 


Navigation and GPS
The modulus helps in determining the separation between two points on a plane when locations are expressed as complex numbers.
 

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Common Mistakes and How to Avoid Them in Modulus of Complex Number

When determining the modulus of a complex number, students frequently make minor errors. Let’s examine what those are and how to quickly resolve them.
 

Mistake 1

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 Neglecting to square both parts
 

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Always square the real and imaginary parts of the numbers, rather than adding them directly under the square root,
For example,
To find |2+6i|, you square both the real part (2) and the imaginary part (6), |2+6i|=22+62 add them to get the answer 40, and then take square root,   40 = 6.3245.
Not 2+6
 

Mistake 2

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 Ignoring negative signs
 

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Always remember, negative values need to be squared correctly.
For example,
|-4+7i|=(-4)2+72 =65 =8.0622 not 42+72 assuming both parts are positive.
 

Mistake 3

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Confusing between conjugate solution and modulus
 

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Always remember, do not substitute the conjugate for the modulus.
For example, the modulus of 8+2i is found by squaring both parts:82+22 =68=8.2462 , and taking square root. Not 8-2i (which is the conjugate).
 

Mistake 4

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Ignoring the step for square root
 

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Keep in mind that after squaring the real and imaginary components and adding them, as in. For example,  
|5-2i| proceed all the way to 52+(-2)2=29=5.3851. To determine the final modulus, you must proceed and take the square root. Do not just write “29” as the answer.
 

Mistake 5

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 Modulus applied to a single component
 

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Always remember to include both the real and imaginary parts. For example, the modulus of |3+2i|=32+22=13=3.605 not just, |2i|=2  which only takes the imaginary portion into account.
 

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Solved Examples on Modulus of Complex Number

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Problem 1

Determine the complex number z=2+6i

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|z|= 6.32455
 

Explanation

|z|=22+62=40=6.32455 To clarify this, the imaginary part is 6 and the real part is 2. Applying the formula |z|=a2+b2, gives us 4+36=40=6.32455
 

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Problem 2

Determine the complex number z=-2-4i

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|z|= 4.4721
 

Explanation

|z|= (-2)2+(-4)2=4+16=20=4.4721 In this case, the imaginary part is -4 and the real part is -2. To find how far this point is from the origin, we square both numbers, add them 4+16=20, then take the square root. So, the modulus is 4.4721. It is like finding the length of a line from the center to the point -2 - 4i
.
 

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Problem 3

Determine the complex number z=6i

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|z|=6 
 

Explanation

For z = 6i, the real part is 0 and the imaginary part is 6. Thus, |z|=02+62=36=6
 

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Problem 4

Determine the complex number z=-9

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|z|=9
 

Explanation

|z|=(-9)2+02=81=9 This number is entirely real. Since the imaginary part is zero, modulus is just the absolute value of the real part.
 

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Problem 5

Determine the complex number z=2-13i

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|z|=13.1529
 

Explanation

|z|=22+(-13)2=4+169=173=13.1529 The imaginary part is -13 and the real part is 2. 173=13.1529 is the result of applying the formula.
 

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FAQs on Modulus of Complex Number

1.What is the modulus formula?

The modulus of a complex number z=a+bi is given by:
|z|=a2+b2.
 

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2.What is the best way to express the modulus of a complex number?

The distance between the origin and the point representing a complex number on the Argand plane is called its modulus. This distance represents the magnitude of the complex number z. Here, let P be the location where the complex number z=x+iy is meant. Then OP = |z|=√(x2+y2).
 

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3.Is a complex number’s modulus always positive?

Yes, a complex number’s modulus is always positive or equal to 0.
 

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4. In complex numbers, what is z?

In complex number, z stands for a number like  z=a+bi, with real part aand imaginary part b. It has a conjugate, z=a-bi which is represented by z in complex numbers.
 

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5.Is 0 a complex number?

Yes, 0 is a complex number because it can be written as 0+0i. Even though it is an ordinary number, it still follows the complex number format, and it is called zero complex number. 
 

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6.How does learning Algebra help students in Philippines make better decisions in daily life?

Algebra teaches kids in Philippines to analyze information and predict outcomes, helping them in decisions like saving money, planning schedules, or solving problems.

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7.How can cultural or local activities in Philippines support learning Algebra topics such as Modulus of Complex Number?

Traditional games, sports, or market activities popular in Philippines can be used to demonstrate Algebra concepts like Modulus of Complex Number, linking learning with familiar experiences.

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8.How do technology and digital tools in Philippines support learning Algebra and Modulus of Complex Number?

At BrightChamps in Philippines, we encourage students to use apps and interactive software to demonstrate Algebra’s Modulus of Complex Number, allowing students to experiment with problems and see instant feedback for better understanding.

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9.Does learning Algebra support future career opportunities for students in Philippines?

Yes, understanding Algebra helps students in Philippines develop critical thinking and problem-solving skills, which are essential in careers like engineering, finance, data science, and more.

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