f(x) =   \frac{ x-a }{ (x-b) (x-c)} 

a = 1 (slider from -5 to 5, step 0.1)
b = 2 (slider from -5 to 5, step 0.1)
c = 0 (slider from -5 to 5, step 0.1)
f(x) = (x - a) / ((x - b) * (x - c))
texto1: "f(x) = " + f