设α=arccos(-根号3/2）则,cosα=-根号3/2α1=150度 (α在第Ⅱ象限）α1＝(5/6)∏α2=210度 (α在第Ⅲ象限) α2=(7/6)∏1.sin[(3/4)∏+(5/6)∏]=sin[∏+(7/12)∏〕原式=-sin(7/12)∏2.sin[(3/4)+(7/6)∏]=sin(23/12)...