1)
a1+3d=a1*d^3
a1+9d=a1*d^9
d^9－3d^3＋2＝0
(d^3+2)*（d^3-1）^2=0d不等于1.则：d=－2^(1/3)
代入求得：a1=2^(1/3)
2）假设是的,是第m项,则：
a1*d^15＝a1+md
m=33
b16是{an}的第34项d^9－3d^3＋2＝0，怎么来的a1+3d=a1*d^3 a1=3d/(d^3-1)a1+9d=a1*d^9 a1=9d/(d^9-1)3d/(d^3-1)=9d/(d^9-1)1/(d^3-1)==3/(d^9-1)d^9-1=3d^3-3d^9－3d^3＋2＝0