f(0) = -3 et f(-1) = -1
Considérons 2 points A et B de coordonnés respectives (0,-3) et (-1,-1)
a = (Yb-Ya)/(Xb-Xa) = (-1-(-3))/(-1-0) = (-1+3)/(-1) = 2/-1 = -2
Fonction affine de coefficient: -2
y = -2x + b
Ya = -2Xa + b
-3 = -2*0 + b
-3 = b
→ y = -2x - 3
