Sagot :
Answer:
Given: a1=9, r=3
Formula: an=ar^n-1
a. ↓↓↓
> a3=(9)(3)^3-1
> a3=(9)(3)^2
> a3=(9)(9)
> a3=81
b. ↓↓↓
Formula: Sn=(1-r^n)/1-r
> S8=(1-(3)^8)/1-3
> S8=(1-6561)/2
> S8=6560/2
> S8=3280
Answer:
Given: a1=9, r=3
Formula: an=ar^n-1
a. ↓↓↓
> a3=(9)(3)^3-1
> a3=(9)(3)^2
> a3=(9)(9)
> a3=81
b. ↓↓↓
Formula: Sn=(1-r^n)/1-r
> S8=(1-(3)^8)/1-3
> S8=(1-6561)/2
> S8=6560/2
> S8=3280