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Which recursive sequence would produce the sequence 
8,-28,80,dots ?

a_(1)=8 and 
a_(n)=-4a_(n-1)-3

a_(1)=8 and 
a_(n)=-3a_(n-1)-4

a_(1)=8 and 
a_(n)=4a_(n-1)-4

a_(1)=8 and 
a_(n)=-4a_(n-1)+4

Which recursive sequence would produce the sequence 8,28,80, 8,-28,80, \ldots ?\newlinea1=8 a_{1}=8 and an=4an13 a_{n}=-4 a_{n-1}-3 \newlinea1=8 a_{1}=8 and an=3an14 a_{n}=-3 a_{n-1}-4 \newlinea1=8 a_{1}=8 and an=4an14 a_{n}=4 a_{n-1}-4 \newlinea1=8 a_{1}=8 and an=4an1+4 a_{n}=-4 a_{n-1}+4

Full solution

Q. Which recursive sequence would produce the sequence 8,28,80, 8,-28,80, \ldots ?\newlinea1=8 a_{1}=8 and an=4an13 a_{n}=-4 a_{n-1}-3 \newlinea1=8 a_{1}=8 and an=3an14 a_{n}=-3 a_{n-1}-4 \newlinea1=8 a_{1}=8 and an=4an14 a_{n}=4 a_{n-1}-4 \newlinea1=8 a_{1}=8 and an=4an1+4 a_{n}=-4 a_{n-1}+4
  1. Identify First Term: Identify the first term of the sequence.\newlineThe first term given is a1=8a_{1} = 8.
  2. Calculate Second Term: Use the first recursive formula to calculate the second term.\newlineThe first option is an=4an13a_{n} = -4a_{n-1} - 3. Let's calculate a2a_{2}:\newlinea2=4a13=4(8)3=323=35a_{2} = -4a_{1} - 3 = -4(8) - 3 = -32 - 3 = -35.\newlineThis does not match the second term of the sequence, which is 28-28.
  3. Calculate Third Term: Use the second recursive formula to calculate the second term.\newlineThe second option is an=3an14a_{n} = -3a_{n-1} - 4. Let's calculate a2a_{2}:\newlinea2=3a14=3(8)4=244=28a_{2} = -3a_{1} - 4 = -3(8) - 4 = -24 - 4 = -28.\newlineThis matches the second term of the sequence.
  4. Verify Pattern - Third Formula: Use the second recursive formula to calculate the third term.\newlineLet's calculate a3a_{3} using the second option:\newlinea3=3a24=3(28)4=844=80a_{3} = -3a_{2} - 4 = -3(-28) - 4 = 84 - 4 = 80.\newlineThis matches the third term of the sequence.
  5. Verify Pattern - Fourth Formula: Verify the pattern with the third recursive formula.\newlineThe third option is an=4an14a_{n} = 4a_{n-1} - 4. Let's calculate a2a_{2}:\newlinea2=4a14=4(8)4=324=28a_{2} = 4a_{1} - 4 = 4(8) - 4 = 32 - 4 = 28.\newlineThis does not match the second term of the sequence, which is 28-28.
  6. Calculate Third Term: Verify the pattern with the fourth recursive formula.\newlineThe fourth option is an=4an1+4a_{n} = -4a_{n-1} + 4. Let's calculate a2a_{2}:\newlinea2=4a1+4=4(8)+4=32+4=28a_{2} = -4a_{1} + 4 = -4(8) + 4 = -32 + 4 = -28.\newlineThis matches the second term of the sequence, but we need to check the third term to be sure.
  7. Calculate Third Term: Verify the pattern with the fourth recursive formula.\newlineThe fourth option is an=4an1+4a_{n} = -4a_{n-1} + 4. Let's calculate a2a_{2}:\newlinea2=4a1+4=4(8)+4=32+4=28a_{2} = -4a_{1} + 4 = -4(8) + 4 = -32 + 4 = -28.\newlineThis matches the second term of the sequence, but we need to check the third term to be sure.Use the fourth recursive formula to calculate the third term.\newlineLet's calculate a3a_{3} using the fourth option:\newlinea3=4a2+4=4(28)+4=112+4=116a_{3} = -4a_{2} + 4 = -4(-28) + 4 = 112 + 4 = 116.\newlineThis does not match the third term of the sequence, which is 8080.

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