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What is the value of [tex]a_1[/tex] in the geometric series?

[tex]\[ \sum_{n=1}^{\infty} 12\left(-\frac{1}{9}\right)^{n-1} \][/tex]

A. [tex]\(-\frac{12}{9}\)[/tex]

B. [tex]\(-\frac{1}{9}\)[/tex]

C. 1

D. 12

Sagot :

Certainly! Let's look at the given geometric series to find the value of the first term [tex]\( a_1 \)[/tex]:

[tex]\[ \sum_{n=1}^{\infty} 12\left(-\frac{1}{9}\right)^{n-1} \][/tex]

In a geometric series, the general form is:

[tex]\[ a + ar + ar^2 + ar^3 + \ldots \][/tex]

Where [tex]\( a \)[/tex] is the first term ([tex]\( a_1 \)[/tex]) and [tex]\( r \)[/tex] is the common ratio.

Here, we're given a series in the form:

[tex]\[ 12 \left(-\frac{1}{9}\right)^{n-1} \][/tex]

To find the first term [tex]\( a_1 \)[/tex], we substitute [tex]\( n = 1 \)[/tex] into the expression. Doing so, we get:

[tex]\[ 12 \left(-\frac{1}{9}\right)^{1-1} \][/tex]

This simplifies to:

[tex]\[ 12 \left(-\frac{1}{9}\right)^0 \][/tex]

Since any number raised to the power of 0 is 1, this further simplifies to:

[tex]\[ 12 \cdot 1 = 12 \][/tex]

Therefore, the value of [tex]\( a_1 \)[/tex] is:
[tex]\[ \boxed{12} \][/tex]