Hello everybody First I'd like to thank for the work all of you are developing with this forum. I found it for casuality but I'm sure since now it will be a perpetual partner. I'm a Spanish Physics graduate and I am working about microwave guides and connectors for devices components in satellites and I have some trouble in my job. Although my questions's title it's not my trouble I think the solution could help for my investigation development. My doubt is about how to change of variable in a Dirac Delta distribution. I know the usually called scaling property: delta[f(x)]=Sum[delta(x-Xi)]/|f´(Xi)| where Xi's are the roots of the function f(x). But my trouble is, for example, in the case that the function is as apparently innocent as f(x)=x^2 because in this case the function has a double root Xi whose value is zero and this is a problem in the denominator of the expression, because f´(Xi)=2*Xi I'd like to receive ideas to solve this problem, although I have a possible way for the beginning. If the function is f(x^2-a^2) with 'a' a real number, the solution is the well-known formula delta[x^2-a^2]=1/(2·|a|)·[delta(x-a)+delta(x+a)] How about if we take the limit 'a' tending to zero? I have no answer to this, but I think it could be an initial idea. I have looked at some books of calculus and I haven't found answer to this problem, but I recognize I have not read all the mathematical books that exist. I am sure my problem is that I have not read the development of this formula to know how adapt it to this case. Thank you for to pay attention.