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Imran and Aubrey were asked to find an explicit formula for the sequence 
14,5,-4,-13,dots, where the first term should be 
g(1).
Imran said the formula is 
g(n)=14-9(n-1).
Aubrey said the formula is 
g(n)=14-9n.
Which one of them is right?
Choose 1 answer:
(A) Only Imran
(B) Only Aubrey
(C) Both Imran and Aubrey
(D) Neither Imran nor Aubrey

Imran and Aubrey were asked to find an explicit formula for the sequence 14,5,4,13, 14,5,-4,-13, \ldots , where the first term should be g(1) g(1) .\newlineImran said the formula is g(n)=149(n1) g(n)=14-9(n-1) .\newlineAubrey said the formula is g(n)=149n g(n)=14-9 n .\newlineWhich one of them is right?\newlineChoose 11 answer:\newline(A) Only Imran\newline(B) Only Aubrey\newline(C) Both Imran and Aubrey\newline(D) Neither Imran nor Aubrey

Full solution

Q. Imran and Aubrey were asked to find an explicit formula for the sequence 14,5,4,13, 14,5,-4,-13, \ldots , where the first term should be g(1) g(1) .\newlineImran said the formula is g(n)=149(n1) g(n)=14-9(n-1) .\newlineAubrey said the formula is g(n)=149n g(n)=14-9 n .\newlineWhich one of them is right?\newlineChoose 11 answer:\newline(A) Only Imran\newline(B) Only Aubrey\newline(C) Both Imran and Aubrey\newline(D) Neither Imran nor Aubrey
  1. Identify type of sequence: Identify the type of sequence. The sequence 14,5,4,13,ext...14, 5, -4, -13, ext{...} has a constant difference between terms, which makes it an arithmetic sequence.
  2. Determine common difference: Determine the common difference dd of the sequence. The difference between the first term 1414 and the second term 55 is 514=95 - 14 = -9. This is the common difference.
  3. Use arithmetic sequence formula: Use the arithmetic sequence formula to find the nth term: g(n)=g(1)+(n1)dg(n) = g(1) + (n-1)d. Here, g(1)g(1) is the first term, which is 1414, and dd is the common difference, which we found to be 9-9.
  4. Substitute values into formula: Substitute the known values into the formula to get Imran's proposed formula: g(n)=14+(n1)(9)g(n) = 14 + (n-1)(-9). Simplify the formula to get g(n)=149(n1)g(n) = 14 - 9(n-1).
  5. Check Imran's formula: Check Imran's formula by plugging in n=2n=2 to see if it gives the second term of the sequence: g(2)=149(21)=149=5g(2) = 14 - 9(2-1) = 14 - 9 = 5. This matches the second term of the sequence, so Imran's formula seems correct so far.
  6. Check Aubrey's formula: Now, check Aubrey's formula by plugging in n=1n=1 to see if it gives the first term of the sequence: g(1)=149(1)=149=5g(1) = 14 - 9(1) = 14 - 9 = 5. This does not match the first term of the sequence, which should be 1414. Therefore, Aubrey's formula is incorrect.
  7. Correct answer: Since Imran's formula gives the correct terms for the sequence and Aubrey's does not, the correct answer is that only Imran is right.

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