A坐标为：x=3cosπ/4,y=3sinπ/4
B坐标为:x=-3cosπ/12,y=-3sinπ/12
AB=√[(3cosπ/4+3cosπ/12)^2+(3sinπ/4+3sinπ/12)^2]
=3√(2+√3)答案为：（3倍根号6+3倍根号2）/2一样的3√(2+√3) ＝3√[(4+2√3)/2]＝3√[(1+√3)^2/2]＝ 3(1+√3)/√2＝3(√6＋√2)/2“AB=√[(3cosπ/4+3cosπ/12)^2+(3sinπ/4+3sinπ/12)^2]=3√(2+√3) ”这一步如何展开呢？请指教，谢谢！sinπ/12＝sin(π/3 -π/4)=sinπ/3cosπ/4-cosπ/3sinπ/4=(√6-√2)/4同理cosπ/12＝(√6+√2)/4代入计算就可以了