2. For each set of voltages, state whether or not the voltages form a balanced three-phase set. If the set is balanced, state whether the phase sequence is positive or

negative. If the set is not balanced, explain why. \text { a) } v_{a}=180 \cos 377 t V, v_{b}=180 \cos \left(377 t-120^{\circ}\right) V, v_{c}=180 \cos \left(377 t-240^{\circ}\right) V \text { c) } v_{a}=-400 \sin 377 t V, v_{b}=400 \sin \left(377 t+210^{\circ}\right) V, v_{c}=400 \cos \left(377 t-30^{\circ}\right) V