2. 布林函數 F(A, B, C) = (A⊕B) ● C + A'●(B⊕C) ，其中⊕表示互斥或(XOR)運算。請問其積之和(SOP)的最簡式？

2. A long coaxial cable (as shown in Fig.) consists of two thin walled concentric conducting cylinders with radii a and b. The inner cylinder carries a steady current i, and the outer cylinder provides the return path for that current. The current sets up a magnetic field between the two cylinders. Calculate the energy stored in the magnetic field for a length l of the cable.