Geometric sequence: an=3(1/2)^(n-1)
First term is 3 and common ratio is 1/2.
Find sum of the first 3 terms, or S3. Either add the first 3 terms or use the formula:
Sn=a1-a1^r^n/1-r. Help on how to do this?! Please!

Question

Geometric sequence: an=3(1/2)^(n-1)
First term is 3 and common ratio is 1/2.
Find sum of the first 3 terms, or S3. Either add the first 3 terms or use the formula: 
Sn=a1-a1^r^n/1-r. Help on how to do this?! Please!

bahrom7893 · Answer

Use this formula:
Sn=a1-a1^r^n/1-r, but just rewrite it what is that?
Sn = (a1-a1^r)^n/(1-r) ?

anonymous · Answer

Yes, the one you typed is correct.

bahrom7893 · Answer

a1 = 3
r = 1/2
n=3
S3 = ?

bahrom7893 · Answer

Substitue all the values u have for Sn formula, wehre
a1=3
r=1/2
n=3

anonymous · Answer

O.k, thank you so much :)