1. The problem statement, all variables and given/known data Two parallel wires are a distance 2 b apart from the origin and carry current I out of the plane of the paper. Find the magnitude and direction of the magnetic field B(y) along the y axis. 2. Relevant equations ∫B⋅dl=μI 3. The attempt at a solution If we take ∫dl = 2πr B=μI/(2πr) r=√(b^2+y^2) Clearly the y components cancel so we are left with only the horizontal components, that is B_total=2Bcos(θ) cos(θ)=b/√(b^2+y^2) However, in the answer key provided, it says that cos(θ)=y/(b^2+y^2) I don't understand why this would give this horizontal component. It seems like this would give the vertical component.