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Since May 2021
Instructor since May 2021
Definition:

A function F defined on the reals is an affine function if and only if it is written in the following form:
F (x) = ax + b, with a and b being reals.

Example:

F (x) = 5x + 8
F (x) = x (here we have: a = 1 and b = 0, or F (x) = 1x + 0)
F (x) = -7x - 5

Counter-example :

F (x) = 2x2 + 6
F (x) = (8 / x) - 5

The form F (x) = ax + b, is not respected

Graphical representation of an affine function:

In a coordinate system, the representation of an affine function is a straight line.

Function variation:

The function has a directing coefficient, it is a. This directing coefficient manages the variation of the line, in fact:
- When a is positive, the line is strictly increasing (it goes up).
- When a is negative, the line is strictly decreasing (it goes down)?
- When a is equal to 0, the line is parallel to the x-axis.

b is the y-intercept of the line. That is to say that the line intersects the y-axis at the point of coordinates (0; b).
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