1. The problem statement, all variables and given/known data Find Bz(0,0,z1), the z component of the magnetic field at the point P located at x=y=0,z=z1 from the current I flowing over a short distance dl = |dl|*j located at the point rc = x1*i. 2. Relevant equations Biot-Savart law: (μo/4∏)*[I*(dL x r)/(|r|^2)] 3. The attempt at a solution I concluded that the radius would be √(( x1 )2 + (z1 )2) and submitted: (μo/4∏)*[I*dL/√(( x1 )2 + (z1 )2)] which was wrong. Then I remember that the equation called for r^2 not r, so I submitted: (μo/4∏)*[I*dL/(( x1 )2 + (z1 )2)] which was also wrong. I thought that the cross product would be even but just in case I tried: (μo/4∏)*[I*-dL/(( x1 )2 + (z1 )2)] which was still wrong. Am I getting the radius wrong? I'm not quite sure what's going on.