mathematics

Henri Delannoy

Henri Delannoy is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Henri Delannoy rather than just read about it. In short: Henri–Auguste Delannoy (French pronunciation: [ɑ̃ʁi oɡyst dəlanwa]; 28 September 1833 – 5 February 1915) was a French army officer and amateur mathematician, after whom the Delannoy numbers are named. Delannoy grew up in Guéret, France, the son of a military accountant.

Key takeaways

Henri Delannoy belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Henri Delannoy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Henri Delannoy from memory before moving on to harder problems.

Reference excerpt

Henri–Auguste Delannoy (French pronunciation: [ɑ̃ʁi oɡyst dəlanwa]; 28 September 1833 – 5 February 1915) was a French army officer and amateur mathematician, after whom the Delannoy numbers are named. Delannoy grew up in Guéret, France, the son of a military accountant. After taking the baccalaureate in 1849, he studied mathematics in Bourges, near where his family lived, and after continuing his studies in Paris entered the École Polytechnique in 1853. He served as a lieutenant in the French artillery in the Second Italian War of Independence, in 1859, and became a captain in 1863. He continued to serve in the military, but shifted from the artillery to the supply corps; he served in Africa, became governor of a military hospital in Algeria, participated in the Franco-Prussian War in 1870, and eventually became an intendant in Orléans before retiring in 1889. His military decorations include the cross and officer's rosette of the Legion of Honour, awarded in 1868 and 1886 respectively. Beginning in 1879, Delannoy began a correspondence with Édouard Lucas on the subject of recreational mathematics and probability theory; he eventually published eleven mathematics articles. Along with his mathematical interests, Delannoy wrote about local history, painted, and from 1896 to 1915 served as the president of the Société des Sciences Naturelles et archéologiques de la Creuse.

References

Illustrations

Henri Delannoy: Henri–Auguste Delannoy — Henri–Auguste Delannoy

Worked examples

Example 1 — a first encounter with Henri Delannoy

Start with the simplest possible case. Write down what Henri Delannoy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Henri Delannoy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Henri Delannoy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Henri Delannoy

In research: Henri Delannoy appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Henri Delannoy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Henri Delannoy is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1833 births, 1915 deaths, French mathematicians, so understanding it makes those chapters shorter.
In everyday life: Look for Henri Delannoy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Henri Delannoy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Henri Delannoy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Henri Delannoy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Henri Delannoy in simple terms?

Why does Henri Delannoy matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Henri Delannoy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Henri Delannoy.