Question

-（2a^2b^3c）^2·2a^2c^2/(-6a^3b^3c)/(3a^2b^3c^3)其中a=-9

Answer 1

Sn=n^2+2n
S(n-1)=(n-1)^2+2(n-1)
an=Sn-S(n-1)=2n+1

bn=2b((n-1)+1
bn+1=2b((n-1)+2=2[b(n-1)+1]
所以bn+1等比，q=2
则bn+1=(b1+1)*2^(n-1)=2^n
所以bn=-1+2^n

Answer 2

=(-4a^6b^4c^6)/(-6a^5b^6c^6)
=2a/(3b^2)
=-6/b^2