Question

What is the sum of the geometric sequence 4,16,64 if there are 8 terms

Answer 1

S(8)=20

Explanation:

Step 1: find the common ratio (constant r)

T(2)/T(1)

=16/4 =4

Step 2: find the first term (constant a)

=4

Step 3: summation of every term in the sequence

By the formula
`S(n)=(a(r^(2)-1 ))/(r-1)`

Substitute a and r

We got
`S(8)=(4(4^(2)-1 ))/(4-1)`

`S(8)=(4(15))/(3)`

`S(8)=(60)/(3)`
`S(8)=20`