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Which recursive sequence would produce the sequence 
3,-19,91,dots ?

a_(1)=3 and 
a_(n)=-6a_(n-1)-1

a_(1)=3 and 
a_(n)=-5a_(n-1)-4

a_(1)=3 and 
a_(n)=-a_(n-1)-6

a_(1)=3 and 
a_(n)=-4a_(n-1)-5

Which recursive sequence would produce the sequence 3,19,91, 3,-19,91, \ldots ?\newlinea1=3 a_{1}=3 and an=6an11 a_{n}=-6 a_{n-1}-1 \newlinea1=3 a_{1}=3 and an=5an14 a_{n}=-5 a_{n-1}-4 \newlinea1=3 a_{1}=3 and an=an16 a_{n}=-a_{n-1}-6 \newlinea1=3 a_{1}=3 and an=4an15 a_{n}=-4 a_{n-1}-5

Full solution

Q. Which recursive sequence would produce the sequence 3,19,91, 3,-19,91, \ldots ?\newlinea1=3 a_{1}=3 and an=6an11 a_{n}=-6 a_{n-1}-1 \newlinea1=3 a_{1}=3 and an=5an14 a_{n}=-5 a_{n-1}-4 \newlinea1=3 a_{1}=3 and an=an16 a_{n}=-a_{n-1}-6 \newlinea1=3 a_{1}=3 and an=4an15 a_{n}=-4 a_{n-1}-5
  1. Identify First Term: Identify the first term of the sequence.\newlineThe first term given is a1=3a_{1} = 3.
  2. Calculate Second Term: Calculate the second term using each recursive formula and compare with the given second term 19-19.\newlineUsing the first formula: an=6an11a_{n} = -6a_{n-1} - 1\newlinea2=6a11=6×31=181=19a_{2} = -6a_{1} - 1 = -6\times3 - 1 = -18 - 1 = -19
  3. Verify Second Term: Verify if the second term calculated in Step 22 matches the given second term.\newlineThe calculated second term using the first formula is 19-19, which matches the given second term.
  4. Calculate Third Term: Calculate the third term using the first recursive formula to verify if it matches the given third term (9191).\newlinea3=6a21=6(19)1=1141=113a_{3} = -6a_{2} - 1 = -6*(-19) - 1 = 114 - 1 = 113
  5. Check Third Term: Check if the third term calculated in Step 44 matches the given third term. The calculated third term using the first formula is 113113, which does not match the given third term (9191).
  6. Test Second Formula: Since the first formula did not produce the correct third term, test the second formula.\newlineUsing the second formula: an=5an14a_{n} = -5a_{n-1} - 4\newlinea2=5a14=5×34=154=19a_{2} = -5a_{1} - 4 = -5\times3 - 4 = -15 - 4 = -19
  7. Verify Second Term: Verify if the second term calculated in Step 66 matches the given second term. The calculated second term using the second formula is 19-19, which matches the given second term.
  8. Calculate Third Term: Calculate the third term using the second recursive formula to verify if it matches the given third term (9191).\newlinea3=5a24=5(19)4=954=91a_{3} = -5a_{2} - 4 = -5*(-19) - 4 = 95 - 4 = 91
  9. Check Third Term: Check if the third term calculated in Step 88 matches the given third term.\newlineThe calculated third term using the second formula is 9191, which matches the given third term.
  10. Final Conclusion: Since the second formula has produced the correct second and third terms, we conclude that this is the correct recursive formula for the sequence.\newlineThe correct recursive sequence formula is a1=3a_{1} = 3 and an=5an14a_{n} = -5a_{n-1} - 4.

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