Finding all the roots at once numerically

I want to calculate the roots of equations like tanh(ax) = x numerically. But the problem is sage gives option of finding just one root provided I give it the interval where the root may be found. (tanh(1.5*x)==x).find_root(0.5,2) But sometimes the interval is not so obvious and I need to know all the numerical roots at once (If the number of roots are finite that is). Is There a way to do that?