1. The problem statement, all variables and given/known data A long, straight wire carries a current of 1.7 A in the +z direction and lies along the line x = –3.0 cm, y = 0. A second such wire carries a current of 1.7 A in the +z direction and lies along the line x = +3.0 cm, y = 0, as shown in Figure. Find the magnetic field at a point P on the y axis at y = 6.0 cm. 2. Relevant equations 3. The attempt at a solution I understood why BL = BR In my textbook, the solution says that vector B is the vector sum of vector BL and vector BR. I don't understand this: It says vector B = -2BL cos (theta) i ( in the -x direction) i is the unit vector here I have no idea where does the -2BL cos (theta) come from!