Hi every one. 1. The problem statement, all variables and given/known data in french,the problem says:"déterminer la force de laplace qui s'exerce entre deux fils de courants réctilignes,indéfinis,parraléles d'intensités I et I' de meme sens".maybe in english it means:"find the laplace force that is applied between two threads of straight currents,undefined,parallel of intenisties I and I' of the same direction" 2. Relevant equations the problem is that in class,we have learned what is the magnetic force that is applied by a thread in a certain point M ,but what about the force applied by a thread on a thread,I think that there will be probably some integrals or some sommations bt I don't know how to do it. 3. The attempt at a solution i tried first to find the magnetic field that each one of these two threads creats in a point of the other thread appling the biot-savart rule,then nafter finding these two forces I will apply the laplace rule,that says that there is a force applied to a conductor in the presence of a magnetic field.the one i was supposed to find before.thanks.