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Which recursive sequence would produce the sequence 
2,3,6,dots ?

a_(1)=2 and 
a_(n)=3a_(n-1)-3

a_(1)=2 and 
a_(n)=-5a_(n-1)+4

a_(1)=2 and 
a_(n)=-3a_(n-1)+3

a_(1)=2 and 
a_(n)=4a_(n-1)-5

Which recursive sequence would produce the sequence 2,3,6, 2,3,6, \ldots ?\newlinea1=2 a_{1}=2 and an=3an13 a_{n}=3 a_{n-1}-3 \newlinea1=2 a_{1}=2 and an=5an1+4 a_{n}=-5 a_{n-1}+4 \newlinea1=2 a_{1}=2 and an=3an1+3 a_{n}=-3 a_{n-1}+3 \newlinea1=2 a_{1}=2 and an=4an15 a_{n}=4 a_{n-1}-5

Full solution

Q. Which recursive sequence would produce the sequence 2,3,6, 2,3,6, \ldots ?\newlinea1=2 a_{1}=2 and an=3an13 a_{n}=3 a_{n-1}-3 \newlinea1=2 a_{1}=2 and an=5an1+4 a_{n}=-5 a_{n-1}+4 \newlinea1=2 a_{1}=2 and an=3an1+3 a_{n}=-3 a_{n-1}+3 \newlinea1=2 a_{1}=2 and an=4an15 a_{n}=4 a_{n-1}-5
  1. Test Formula 11: Let's test each recursive formula by applying it to the given initial value and checking if it produces the sequence 2,3,6,2, 3, 6, \ldots .\newlineWe start with the first option:\newlinea1=2a_{1}=2 and \newlinean=3an13a_{n}=3a_{n-1}-3\newlineWe know a1=2a_{1}=2, so let's find a2a_{2}:\newlinea2=3a13a_{2}=3a_{1}-3\newlinea2=3×23a_{2}=3\times 2-3\newlinea2=63a_{2}=6-3\newlinea2=3a_{2}=3\newlineNow let's find a3a_{3}:\newlinea1=2a_{1}=200\newlinea1=2a_{1}=211\newlinea1=2a_{1}=222\newlinea1=2a_{1}=233\newlineSo far, the sequence matches: a1=2a_{1}=244. Let's check one more term to be sure.\newlinea1=2a_{1}=255\newlinea1=2a_{1}=266\newlinea1=2a_{1}=277\newlinea1=2a_{1}=288\newlineThe sequence we have from this formula is a1=2a_{1}=299, which does not match the expected sequence of an=3an13a_{n}=3a_{n-1}-300 because the next term should be a multiple of the previous term, not an=3an13a_{n}=3a_{n-1}-311.
  2. Test Formula 22: Let's test the second option:\newlinea1=2a_{1}=2 and \newlinean=5an1+4a_{n}=-5a_{n-1}+4\newlineWe know a1=2a_{1}=2, so let's find a2a_{2}:\newlinea2=5a1+4a_{2}=-5a_{1}+4\newlinea2=5×2+4a_{2}=-5\times 2+4\newlinea2=10+4a_{2}=-10+4\newlinea2=6a_{2}=-6\newlineThis does not match the second term of the sequence, which is 33, so this option is incorrect.
  3. Test Formula 33: Let's test the third option:\newlinea1=2a_{1}=2 and \newlinean=3an1+3a_{n}=-3a_{n-1}+3\newlineWe know a1=2a_{1}=2, so let's find a2a_{2}:\newlinea2=3a1+3a_{2}=-3a_{1}+3\newlinea2=3×2+3a_{2}=-3\times 2+3\newlinea2=6+3a_{2}=-6+3\newlinea2=3a_{2}=-3\newlineThis does not match the second term of the sequence, which is 33, so this option is incorrect.
  4. Test Formula 44: Finally, let's test the fourth option:\newlinea1=2a_{1}=2 and \newlinean=4an15a_{n}=4a_{n-1}-5\newlineWe know a1=2a_{1}=2, so let's find a2a_{2}:\newlinea2=4a15a_{2}=4a_{1}-5\newlinea2=4×25a_{2}=4\times 2-5\newlinea2=85a_{2}=8-5\newlinea2=3a_{2}=3\newlineNow let's find a3a_{3}:\newlinea3=4a25a_{3}=4a_{2}-5\newlinean=4an15a_{n}=4a_{n-1}-500\newlinean=4an15a_{n}=4a_{n-1}-511\newlinean=4an15a_{n}=4a_{n-1}-522\newlineThis does not match the third term of the sequence, which is an=4an15a_{n}=4a_{n-1}-533, so this option is incorrect.

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