解
(a+3i)/i=b+i這個吧
左邊分子分母同時乘以i得：
(a+3i)i/(i×i)=b+i
得：-(a+3i)i=b+i
即-ai+3=b+i
∴b=3,a=-1
∴ab=3×(-1)=-3?????????????A????-1??1??0??B????y??y??cos????x??x??A????A??B??x=-1????y=cos(-??)=-1x=1????y=cos??=-1x=0????y=cos0=1??B={-1??1}A??B={-1.1}