30.若電壓v(t)＝50sin(?t＋45°)V，電流i(t)＝10cos(?t－45°)A，則下列何者錯誤？ (A) v(t)領先i(t) 90° (B) v(t)落後i(t) 90° (C) v(t)領先i(t) 180° (D) v(t)與i(t)同相