an=a1+(n-1)d點(an,bn)在函數(shù)f(x)=2^x的圖像上bn=2^(an) = 2^(a1+(n-1)d ) (1)(1)a1=1(a8,4b1)在函數(shù)f(x)的圖像上4b1= 2^(a8)= 2^(1+7d) (2)from (1)put n=1b1=2 (3)sub (3) into (2)8=2^(1+7d)1+7d=3d=-2/7an = 1-(...太謝謝了??！ 額 那個我打錯了一個地方……那個點是 （a8,4b7)……能不能再做一下？ 謝謝 ~\(≧▽≦)/~an=a1+(n-1)d

點(an,bn)在函數(shù)f(x)=2^x的圖像上
bn=2^(an) = 2^(a1+(n-1)d ) (1)
(1)
a1=1
(a8,4b7)在函數(shù)f(x)的圖像上
4b7= 2^(a8)
= 2^(1+7d)

from (1)，put n=7
b7=2^(1+6d) (3)

sub (3) into (2)
4. 2^(1+6d)=2^(1+7d)
2^(3+6d)=2^(1+7d)
3+6d =1+7d
d=2
an = 1+2(n-1) =2n-1
Sn = n^2
第二部分是一樣