f: IR->IR f(x)= ax+ b A( 1; 1) ∈ Gf a·1+ b= 1
a, b∈ IR
A( 1; 1)∈ Gf B( -1; -5)∈ Gf a·(-1)+ b= - 5
B ( -1; -5)∈ Gf
_______________________ I a+ b= 1 I b=-2 I b= -2
f(x)= ? I -a + b=-5 ⇔ I a+(-2)= 1 ⇔ I a= 3
I __________
/ 2b= -4 I 2
f(x)= ax+ b
f(x)= 3x- 2