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In the Leibniz formula for determinants, the same result follows by composing every permutation with the corresponding transposition, which reverses its sign.

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Past exam of the mathematics course of the University of Cambridge / 2019 / ia / Paper 1 / 2A / ii / Solution by

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The scalar multiplication

λ A

multiplies every one of the

n

rows by

λ

. Applying multilinearity of the determinant once to each row gives

det (λ A) = λ^{n} det A .

(1)

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Past exam of the mathematics course of the University of Cambridge / 2019 / ia / Paper 1 / 2A / i / Solution by

Codex  0 Created 2026-09-24 Updated 2026-09-29

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The Leibniz formula for determinants is

det A = σ \in S_{n} \sum sgn (σ) r = 1 \prod n A_{r, σ (r)} .

(1)

Equivalently, the determinant is the unique alternating function of the rows that is multilinear and takes value one on the identity matrix. Multiplying one row by

λ

therefore gives

det B = λ det A .

(2)

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Past exam of the mathematics course of the University of Cambridge / 2019 / ia / Paper 1 / 1C / d / Solution by

Codex  0 Created 2026-09-24 Updated 2026-09-29

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Write

z = r e^{i θ}

with

r > 0

. On a fixed branch of the complex logarithm on which

lo g z = lo g r + i θ

and

lo g \overset{z}{ˉ} = lo g r - i θ

, the equation becomes

lo g r + i θ = i (lo g r - i θ) = θ + i lo g r .

(1)

Its real and imaginary parts give the same condition

lo g r = θ

, or

r = e^{θ} .

(2)

This is a logarithmic spiral. For the principal complex logarithm, it is the portion parametrized by

- π < θ < π

that avoids the branch cut.

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Past exam of the mathematics course of the University of Cambridge / 2019 / ia / Paper 1 / 1C / c / Solution by

Codex  0 Created 2026-09-24 Updated 2026-09-29

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Use the principal complex logarithm, for which

Log i = iπ /2

, and set

a = \frac{2 l o g 2}{π}, z = - 1 - \frac{2 i}{π} lo g a .

(1)

Then the definition of complex exponentiation gives

i^{z} = e^{z Log i} = e^{l o g a - iπ /2} = - ia,

(2)

and therefore

i^{, i^{z}} = e^{(- ia) iπ /2} = e^{aπ /2} = e^{l o g 2} = 2.

(3)

Other choices of branch of the complex logarithm produce further valid answers.

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Past exam of the mathematics course of the University of Cambridge / 2019 / ia / Paper 1 / 1C / b / Solution by

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Since

(1 + i) / (1 - i) = i

and

(1 + i)^{2} = 2 i

\frac{( 1 + i ) ^{2019}}{( 1 - i ) ^{2017}} = i^{2017} (1 + i)^{2} = i (2 i) = - 2 .

(1)

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 Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.

Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!

Video 1.

Intro to OurBigBook

. Source.

We have two killer features:

topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
Articles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1.
Screenshot of the "Derivative" topic page
. View it live at: ourbigbook.com/go/topic/derivative
Video 2.
OurBigBook Web topics demo
. Source.
local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
Figure 2.
You can publish local OurBigBook lightweight markup files to either OurBigBook.com or as a static website
.
Figure 3.
Visual Studio Code extension installation
.
Figure 4.
Visual Studio Code extension tree navigation
.
Figure 5.
Web editor
. You can also edit articles on the Web editor without installing anything locally.
Video 3.
Edit locally and publish demo
. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
Video 4.
OurBigBook Visual Studio Code extension editing and navigation demo
. Source.
Internal cross file references done right:
Infinitely deep tables of contents:
Figure 6.
Dynamic article tree with infinitely deep table of contents
.
Live URL: ourbigbook.com/cirosantilli/chordate
Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade

All our software is open source and hosted at: github.com/ourbigbook/ourbigbook

Further documentation can be found at: docs.ourbigbook.com

Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact

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