The rule that defines S for [tex]a_n = 3(0.7)^n[/tex] is:
[tex]S_n = 7(1 - 0.7^n)[/tex]
The rule of S means that we calculate the rule that defines the sum of n terms of the geometric progression.
Given that:
[tex]a_n = 3(0.7)^n[/tex]
Rewrite as:
[tex]a_n = 3 (0.7)^n \times 1[/tex]
Replace 1 with 0.7/0.7
[tex]a_n = 3 (0.7)^n \times \frac{0.7}{0.7}[/tex]
Rewrite as:
[tex]a_n = 3 *0.7 \times \frac{(0.7)^n}{0.7}[/tex]
Apply law of indices
[tex]a_n = 3 \times 0.7 \times (0.7)^{n-1}[/tex]
[tex]a_n = 2.1 \times (0.7)^{n-1}[/tex]
The n term of a geometric progression is:
[tex]a_n = ar^{n-1}[/tex]
Compare [tex]a_n = ar^{n-1}[/tex] to [tex]a_n = 2.1 \times (0.7)^{n-1}[/tex]
[tex]a = 2.1[/tex] --- the first term
[tex]r = 0.7[/tex]
The sum of n terms of a geometric progression is:
[tex]S_n = \frac{a(1 - r^n)}{1 -r}[/tex]
This gives:
[tex]S_n = \frac{2.1(1 - 0.7^n)}{1 -0.7}[/tex]
[tex]S_n = \frac{2.1(1 - 0.7^n)}{0.3}[/tex]
[tex]S_n = 7(1 - 0.7^n)[/tex]
Learn more about the sum of geometric progression at:
https://brainly.com/question/22068689
