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NECO 2024 · Paper 1 · Q5

The third term of a geometric progression is −5-5 and the seventh term is −80-80. Find the common ratio.

Worked solution (try it first)
  1. The 3rd term is ar2=−5ar^2 = -5 and the 7th is ar6=−80ar^6 = -80.
  2. Divide: r4=−80−5=16r^4 = \frac{-80}{-5} = 16.
  3. Take the fourth root: r=±2r = \pm 2, and the option is r=2r = 2, option E.

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