Hey guys I have a wire oriented along the x axis with lengths -L/2 to L/2 The first part of the Biot Savart formula has a I dl in vector notation crossed with (r-r')/(r-r')^3. I used I(i hat) for the I dl vector and to cross it, i used r as my observation point and r' as source. When I did the integral where the observation point D is located at D j(hat) i got a negative B oriented in the k (hat) axis. Now according to the answer and picture it should be positive. Can you please give me tips on how to determine my I dl vector and maybe I flipped the r and r' and it should be source - observation point??