..初中问题?
n=1
a2=pa1+q
3=p+q.(1)
n=2
a3=pa2+q
n=3
a4=pa3+q=p(pa2+q)+q=3p*p+p*q+q.(2)
(1)(2)联立
-〉p=2 q=1 or p=-3 q=6