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Write out the first five terms of the sequence [tex]b_n = 400 \cdot \left(-\frac{1}{2}\right)^{n-1}[/tex].

A. [tex]-200, 100, -50, 25, -\frac{25}{2}[/tex]

B. [tex]200, -100, 50, -25, \frac{25}{2}[/tex]

C. [tex]400, -200, 100, -50, 25[/tex]

D. [tex]-1, -200, -100, -50, -25[/tex]

Answer :

To find the first five terms of the sequence given by the formula [tex]\( b_n = 400 \cdot \left(-\frac{1}{2}\right)^{n-1} \)[/tex], we'll evaluate this expression for the first five positive integer values of [tex]\( n \)[/tex].

Step-by-step calculation:

1. First Term ([tex]\( n = 1 \)[/tex]):
[tex]\[
b_1 = 400 \cdot \left(-\frac{1}{2}\right)^{1-1} = 400 \cdot \left(-\frac{1}{2}\right)^0 = 400 \cdot 1 = 400
\][/tex]

2. Second Term ([tex]\( n = 2 \)[/tex]):
[tex]\[
b_2 = 400 \cdot \left(-\frac{1}{2}\right)^{2-1} = 400 \cdot \left(-\frac{1}{2}\right)^1 = 400 \cdot \left(-\frac{1}{2}\right) = -200
\][/tex]

3. Third Term ([tex]\( n = 3 \)[/tex]):
[tex]\[
b_3 = 400 \cdot \left(-\frac{1}{2}\right)^{3-1} = 400 \cdot \left(-\frac{1}{2}\right)^2 = 400 \cdot \frac{1}{4} = 100
\][/tex]

4. Fourth Term ([tex]\( n = 4 \)[/tex]):
[tex]\[
b_4 = 400 \cdot \left(-\frac{1}{2}\right)^{4-1} = 400 \cdot \left(-\frac{1}{2}\right)^3 = 400 \cdot \left(-\frac{1}{8}\right) = -50
\][/tex]

5. Fifth Term ([tex]\( n = 5 \)[/tex]):
[tex]\[
b_5 = 400 \cdot \left(-\frac{1}{2}\right)^{5-1} = 400 \cdot \left(-\frac{1}{2}\right)^4 = 400 \cdot \frac{1}{16} = 25
\][/tex]

So, the first five terms of the sequence are [tex]\( 400, -200, 100, -50, \)[/tex] and [tex]\( 25 \)[/tex].

The correct answer is C. [tex]\( 400, -200, 100, -50, 25 \)[/tex].

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