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Which recursive sequence would produce the sequence 
7,33,163,dots ?

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

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

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

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

Which recursive sequence would produce the sequence 7,33,163, 7,33,163, \ldots ?\newlinea1=7 a_{1}=7 and an=5an12 a_{n}=5 a_{n-1}-2 \newlinea1=7 a_{1}=7 and an=5an1+4 a_{n}=5 a_{n-1}+4 \newlinea1=7 a_{1}=7 and an=4an1+5 a_{n}=4 a_{n-1}+5 \newlinea1=7 a_{1}=7 and an=2an1+5 a_{n}=-2 a_{n-1}+5

Full solution

Q. Which recursive sequence would produce the sequence 7,33,163, 7,33,163, \ldots ?\newlinea1=7 a_{1}=7 and an=5an12 a_{n}=5 a_{n-1}-2 \newlinea1=7 a_{1}=7 and an=5an1+4 a_{n}=5 a_{n-1}+4 \newlinea1=7 a_{1}=7 and an=4an1+5 a_{n}=4 a_{n-1}+5 \newlinea1=7 a_{1}=7 and an=2an1+5 a_{n}=-2 a_{n-1}+5
  1. Identify First Term: Identify the first term of the sequence.\newlineThe first term given is a1=7a_{1} = 7.
  2. Find Second Term: Use the first recursive formula to find the second term.\newlineThe first option is an=5an12a_{n} = 5a_{n-1} - 2. Let's apply it to find a2a_{2}.\newlinea2=5×a12=5×72=352=33a_{2} = 5 \times a_{1} - 2 = 5 \times 7 - 2 = 35 - 2 = 33.\newlineThis matches the second term of the sequence.
  3. Find Third Term: Use the first recursive formula to find the third term.\newlineNow, let's find a3a_{3} using the same formula.\newlinea3=5×a22=5×332=1652=163a_{3} = 5 \times a_{2} - 2 = 5 \times 33 - 2 = 165 - 2 = 163.\newlineThis matches the third term of the sequence.
  4. Verify Other Options: Verify that the other options do not match the sequence.\newlineTo ensure we have the correct formula, we should check that the other options do not produce the sequence.\newlineFor the second option, an=5an1+4a_{n} = 5a_{n-1} + 4, let's find a2a_{2}.\newlinea2=5×a1+4=5×7+4=35+4=39a_{2} = 5 \times a_{1} + 4 = 5 \times 7 + 4 = 35 + 4 = 39.\newlineThis does not match the second term of the sequence.
  5. Check Second Option: Check the third option.\newlineFor the third option, an=4an1+5a_{n} = 4a_{n-1} + 5, let's find a2a_{2}.\newlinea2=4×a1+5=4×7+5=28+5=33a_{2} = 4 \times a_{1} + 5 = 4 \times 7 + 5 = 28 + 5 = 33.\newlineThis matches the second term of the sequence, so we need to check the third term.
  6. Check Third Option: Find the third term using the third option.\newlinea3=4×a2+5=4×33+5=132+5=137a_{3} = 4 \times a_{2} + 5 = 4 \times 33 + 5 = 132 + 5 = 137.\newlineThis does not match the third term of the sequence.
  7. Check Fourth Option: Check the fourth option.\newlineFor the fourth option, an=2an1+5a_{n} = -2a_{n-1} + 5, let's find a2a_{2}.\newlinea2=2×a1+5=2×7+5=14+5=9a_{2} = -2 \times a_{1} + 5 = -2 \times 7 + 5 = -14 + 5 = -9.\newlineThis does not match the second term of the sequence.
  8. Conclude Correct Formula: Conclude the correct recursive formula.\newlineSince only the first option produces the correct second and third terms of the sequence, we can conclude that the correct recursive formula is:\newlinea1=7a_{1} = 7 and an=5an12a_{n} = 5a_{n-1} - 2.

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