## Manipulation of Sums Using the Sigma Symbol

Manipulation of sums via the symbol (sigma), is based on a small number of rules. The purpose of this article is to list them and give examples of their use, without any claim to originality. Sigma To begin, let’s ask about the interest of the notation . 1 – Abandonment of the Suspension Points Reading the

## What is a conjecture in mathematics?

1 – Very first numbers … or not! Consider, for each natural integer , the integer: conjecture     We can easily calculate: conjecture     And so on \ldots{} With a little habit, something strange challenges us … These numbers are all first.

## What is a factorial?

1 – Five books to read … but in what order? factorial You are about to go on vacation … factorial As you like to read novels, you are about to choose five to devour at night, comfortably installed in a quiet place. Once the books are selected, a question remains: in what order are you going

## Direct Image / Reciprocal Image of a Part

Some notions on the scientific CPGE program are less easy to assimilate than others. If a list of the 10 concepts that pose the greatest difficulty for students is drawn up, I can say from experience that the notion of direct image or mutual image would figure prominently. Direct Image The purpose of this note is

## What is a bijection?

1 – Informal description of the concept of bijection It’s decided, I have my collection of old books appraised! bijection To prepare the ground, you have to label each book and give it a serial number. As I have a set of labels (with a number written on each one), it’s going to be a breeze.