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The general term of an infinite sequence 9, 4, -1, -6,... is \(u_{r} = ar...

Further Mathematics
WAEC 2018

The general term of an infinite sequence 9, 4, -1, -6,... is \(u_{r} = ar + b\). Find the values of a and b.

  • A. a = 5, b = 14
  • B. a = -5, b = 14
  • C. a = 5, b = -14
  • D. a = -5, b = -14
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Correct Answer: Option B
Explanation

The terms of the sequence can be written as : \(u_{r} = ar + b\) in this case, being that they have a regular common difference for each of the r terms.

We can rewrite the sequence as \(a + b, 2a + b, 3a + b,...\) where a is the common difference of the sequence and b is a given constant gotten by solving

\(a + b = 9\) or \(2a + b = 4\) or any other one. 

The common difference here is 4 - 9 = -1 - 4 = -5.

\(-5 + b = 9 \implies b = 9 + 5 = 14\)

\(\therefore\) The equation can be written as \(u_{r} = -5r + 14\).


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WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC offline past questions - with all answers and explanations in one app - Download for free