set terminal fig color big portrait set output "exer01.01.01.fig" set xrange [-5:5] f(x) = x**3 - 3*x**2 - 9*x + 2 a = -4 df(x) = 3*x**2 - 6*x - 9 reta(x) = f(a) + df(a)*(x-a) plot f(x),0, reta(x)