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Ivy and Andrey were asked to find an explicit formula for the sequence [tex]\(-100, -50, 0, 50, \ldots\)[/tex], where the first term should be [tex]\(f(1)\)[/tex].

Ivy said the formula is [tex]\(f(n) = -100 + 50(n - 1)\)[/tex].
Andrey said the formula is [tex]\(f(n) = -150 + 50n\)[/tex].

Which one of them is right?

Choose 1 answer:
A. Only Ivy
B. Only Andrey
C. Both Ivy and Andrey
D. Neither Ivy nor Andrey


Sagot :

To determine which of Ivy and Andrey provided the correct formula for the sequence [tex]\(-100, -50, 0, 50, \ldots\)[/tex], we will verify both of their formulas step-by-step.

### Step-by-Step Solution:

1. Examine Ivy's Formula: [tex]\( f(n) = -100 + 50(n - 1) \)[/tex]

Let's calculate the first few terms using Ivy's formula:
- For [tex]\( n = 1 \)[/tex]:
[tex]\[ f(1) = -100 + 50(1 - 1) = -100 + 0 = -100 \][/tex]
- For [tex]\( n = 2 \)[/tex]:
[tex]\[ f(2) = -100 + 50(2 - 1) = -100 + 50 = -50 \][/tex]
- For [tex]\( n = 3 \)[/tex]:
[tex]\[ f(3) = -100 + 50(3 - 1) = -100 + 100 = 0 \][/tex]
- For [tex]\( n = 4 \)[/tex]:
[tex]\[ f(4) = -100 + 50(4 - 1) = -100 + 150 = 50 \][/tex]

Ivy's formula matches the given sequence [tex]\(-100, -50, 0, 50\)[/tex].

2. Examine Andrey's Formula: [tex]\( f(n) = -150 + 50n \)[/tex]

Now, let's calculate the first few terms using Andrey's formula:
- For [tex]\( n = 1 \)[/tex]:
[tex]\[ f(1) = -150 + 50(1) = -150 + 50 = -100 \][/tex]
- For [tex]\( n = 2 \)[/tex]:
[tex]\[ f(2) = -150 + 50(2) = -150 + 100 = -50 \][/tex]
- For [tex]\( n = 3 \)[/tex]:
[tex]\[ f(3) = -150 + 50(3) = -150 + 150 = 0 \][/tex]
- For [tex]\( n = 4 \)[/tex]:
[tex]\[ f(4) = -150 + 50(4) = -150 + 200 = 50 \][/tex]

Andrey's formula also matches the given sequence [tex]\(-100, -50, 0, 50\)[/tex].

Since both formulas, [tex]\( f(n) = -100 + 50(n - 1) \)[/tex] by Ivy and [tex]\( f(n) = -150 + 50n \)[/tex] by Andrey, correctly produce the given sequence, the right answer is:

(C) Both Ivy and Andrey
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