It is always possible to formulate electromagnetism with a divergence-free magnetic vector potential. Write down the gauge transformation that achieves this result.(2) Show further that with this gauge choice, the scalar potential always satisfies Poisson's equation.(2) Finally, show that, for a constant and uniform magnetic field B, the expression Á = --1/2r xB provides a solution for the magnetic vector potential that satisfies2 this gaugechoice.(3)