Background image of landing

Unrivalled
Education
Solutions for your
Family

How to calculate the common logarithm of a complex number?

To compute the common logarithm of a complex number, we first need to convert it into polar form.

Start by expressing the complex number in the standard form ( a + bi ), where ( a ) and ( b ) are real numbers and ( i ) is the imaginary unit. Next, we calculate the modulus ( r ) and the argument ( \theta ) of the complex number using the following formulas:

r=a2+b2r = \sqrt{a^2 + b^2} θ=tan1(ba)\theta = \tan^{-1}\left(\frac{b}{a}\right)

After determining ( r ) and ( \theta ), we can represent the complex number in polar form as:

r(cosθ+isinθ)r \left( \cos \theta + i \sin \theta \right)

Finally, we can find the common logarithm of the complex number using the formula:

log(z)=log(r)+iθ\log(z) = \log(r) + i\theta

Example:

Let’s find the common logarithm of the complex number ( 2 + 3i ):

  1. Calculate the modulus ( r ):
r=22+32=4+9=13r = \sqrt{2^2 + 3^2} = \sqrt{4 + 9} = \sqrt{13}
  1. Next, calculate the argument ( \theta ):
θ=tan1(32)56.31\theta = \tan^{-1}\left(\frac{3}{2}\right) \approx 56.31^\circ

Thus, the complex number in polar form is:

13(cos(56.31)+isin(56.31))\sqrt{13} \left( \cos(56.31^\circ) + i \sin(56.31^\circ) \right)

Using the logarithm formula, we can compute the common logarithm:

log(2+3i)=log(13)+i56.31\log(2 + 3i) = \log(\sqrt{13}) + i \cdot 56.31^\circ

To express ( \log(\sqrt{13}) ):

log(13)=12log(13)0.1139\log(\sqrt{13}) = \frac{1}{2} \log(13) \approx 0.1139

Therefore, we obtain:

log(2+3i)0.1139+i56.31\log(2 + 3i) \approx 0.1139 + i \cdot 56.31^\circ

To express the argument in terms of natural logarithm:

log(2+3i)=0.1139+i56.31log(10)0.1139+i0.8686\log(2 + 3i) = 0.1139 + i \cdot \frac{56.31^\circ}{\log(10)} \approx 0.1139 + i \cdot 0.8686

Thus, the common logarithm of ( 2 + 3i ) is approximately:

0.1139+i0.86860.1139 + i \cdot 0.8686
Answered by: Prof. Alan Smith
A-Level Physics Tutor
Medal Icon

100%

Globe Icon

Global

Crest Icon

97%

Professional Tutors

International Tuition

Independent School Entrance Success

All of our elite tutors are full-time professionals, with at least five years of tuition experience and over 5000 accrued teaching hours in their subject.

Based in Cambridge, with operations spanning the globe, we can provide our services to support your family anywhere.

Our families consistently gain offers from at least one of their target schools, including Eton, Harrow, Wellington and Wycombe Abbey.

Medal Icon

100%

Professional Tutors

All of our elite tutors are full-time professionals, with at least five years of tuition experience and over 5000 accrued teaching hours in their subject.

Globe Icon

Global

International Tuition

Based in Cambridge, with operations spanning the globe, we can provide our services to support your family anywhere.

Crest Icon

97%

Independent School Entrance Success

Our families consistently gain offers from at least one of their target schools, including Eton, Harrow, Wellington and Wycombe Abbey.

Book a free
30-minute consultation
session

At the Beyond Tutors we recognise that no two students are the same. 

That’s why we’ve transcended the traditional online tutoring model of cookie-cutter solutions to intricate educational problems. Instead, we devise a bespoke tutoring plan for each individual student, to support you on your path to academic success.

To help us understand your unique educational needs, we provide a free 30-minute consultation with one of our founding partners, so we can devise the tutoring plan that’s right for you.

To ensure we can best prepare for this consultation, we ask you to fill out the short form below.

Hire a Tutor

All the form fields are optional, but we ask you to provide as much information as possible so that we are in a better position to quickly meet your tutoring requirements.

Still have questions?
Let's get in touch