Which one is the general term for a G.P. with [tex]G_1 = \frac{1}{2}[/tex] and [tex]r = \frac{1}{2}[/tex]?

A. [tex]2^{-n}[/tex]
B. [tex](-2)^n[/tex]
C. [tex](-2)^{n-1}[/tex]
D. [tex]2^{-n-1}[/tex]



Answer :

To solve for the general term of a geometric progression (G.P.), we start with the essential formula for the [tex]\(n\)[/tex]-th term [tex]\(G(n)\)[/tex] of a geometric progression:

[tex]\[ G(n) = G_1 \cdot r^{n-1} \][/tex]

where:
- [tex]\(G_1\)[/tex] is the first term of the G.P.
- [tex]\(r\)[/tex] is the common ratio.
- [tex]\(n\)[/tex] is the term number.

Given:
- The first term [tex]\(G_1\)[/tex] is [tex]\(\frac{1}{2}\)[/tex].
- The common ratio [tex]\(r\)[/tex] is [tex]\(\frac{1}{2}\)[/tex].

Let's substitute these values into our formula:

[tex]\[ G(n) = \left(\frac{1}{2}\right) \cdot \left(\frac{1}{2}\right)^{n-1} \][/tex]

To simplify this expression, we need to combine the fractions:

[tex]\[ G(n) = \left(\frac{1}{2}\right) \cdot \left(\frac{1}{2}\right)^{n-1} \][/tex]
[tex]\[ G(n) = \frac{1}{2} \cdot \frac{1^{n-1}}{2^{n-1}} \][/tex]
[tex]\[ G(n) = \frac{1}{2} \cdot \frac{1}{2^{n-1}} \][/tex]
[tex]\[ G(n) = \frac{1}{2 \cdot 2^{n-1}} \][/tex]
[tex]\[ G(n) = \frac{1}{2^n} \][/tex]

This simplifies further to:

[tex]\[ G(n) = 2^{-n} \][/tex]

Thus, the general term [tex]\(G(n)\)[/tex] for this geometric progression is [tex]\(2^{-n}\)[/tex].

Therefore, the correct answer is:
A. [tex]\(2^{-n}\)[/tex]