高一数学计算：sin420°cos750°+sin(
计算：sin420°c750°+sin(-690°)cos(-660°) 需要具体过程和答案
sin420°cos750°+sin(-690°)cos(-660°) =sin(360+60)cos(720+30)+sin(-720+30)cos(-720+60) =3/4-1/4 =1/2