f(x)= 2.x
f(x)= 3.x -2
f(x)= 2.x - 4
f (x)= 3.x + 4
f(x)= 1/3.x
f(x)= 2.x + 2/5
f(x)= x +1
f(x)= - 1 /3 . x -3
f(x)= - x
