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Which recursive sequence would produce the sequence 
7,-33,167,dots ?

a_(1)=7 and 
a_(n)=2a_(n-1)-5

a_(1)=7 and 
a_(n)=-5a_(n-1)+2

a_(1)=7 and 
a_(n)=-4a_(n-1)-5

a_(1)=7 and 
a_(n)=-5a_(n-1)-4

Which recursive sequence would produce the sequence 7,33,167, 7,-33,167, \ldots ?\newlinea1=7 a_{1}=7 and an=2an15 a_{n}=2 a_{n-1}-5 \newlinea1=7 a_{1}=7 and an=5an1+2 a_{n}=-5 a_{n-1}+2 \newlinea1=7 a_{1}=7 and an=4an15 a_{n}=-4 a_{n-1}-5 \newlinea1=7 a_{1}=7 and an=5an14 a_{n}=-5 a_{n-1}-4

Full solution

Q. Which recursive sequence would produce the sequence 7,33,167, 7,-33,167, \ldots ?\newlinea1=7 a_{1}=7 and an=2an15 a_{n}=2 a_{n-1}-5 \newlinea1=7 a_{1}=7 and an=5an1+2 a_{n}=-5 a_{n-1}+2 \newlinea1=7 a_{1}=7 and an=4an15 a_{n}=-4 a_{n-1}-5 \newlinea1=7 a_{1}=7 and an=5an14 a_{n}=-5 a_{n-1}-4
  1. Identify First Term: Identify the first term of the sequence.\newlineThe first term given is a1=7a_{1} = 7.
  2. Test First Formula: Use the second term to test the recursive formulas.\newlineThe second term in the sequence is 33-33. We will substitute n=2n = 2 into each recursive formula to see which one yields 33-33 when the first term is 77.\newlineFor the first formula:\newlinea2=2a15a_{2} = 2a_{1} - 5\newlinea2=2(7)5a_{2} = 2(7) - 5\newlinea2=145a_{2} = 14 - 5\newlinea2=9a_{2} = 9\newlineThis does not match the second term of the sequence, which is 33-33.
  3. Test Second Formula: Test the second recursive formula.\newlineFor the second formula:\newlinea2=5a1+2a_{2} = -5a_{1} + 2\newlinea2=5(7)+2a_{2} = -5(7) + 2\newlinea2=35+2a_{2} = -35 + 2\newlinea2=33a_{2} = -33\newlineThis matches the second term of the sequence.
  4. Verify Third Term: Verify the third term using the correct formula from Step 33.\newlineThe third term in the sequence is 167167. We will now check if this term can be obtained by applying the recursive formula an=5an1+2a_{n} = -5a_{n-1} + 2 with n=3n = 3.\newlinea3=5a2+2a_{3} = -5a_{2} + 2\newlinea3=5(33)+2a_{3} = -5(-33) + 2\newlinea3=165+2a_{3} = 165 + 2\newlinea3=167a_{3} = 167\newlineThis matches the third term of the sequence.
  5. Conclude Correct Formula: Conclude that the correct recursive formula is found.\newlineSince the recursive formula an=5an1+2a_{n} = -5a_{n-1} + 2 produces the correct second and third terms of the sequence when starting with a1=7a_{1} = 7, we can conclude that this is the correct recursive formula for the given sequence.

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