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).