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WAEC 2020 · Paper 1 · Q23

Find the nnth term of the linear sequence (A.P.) (5y+1),(2y+1),(1−y),…(5y + 1), (2y + 1), (1 - y), \dots

Worked solution (try it first)
  1. The common difference is d=(2y+1)−(5y+1)=−3yd = (2y + 1) - (5y + 1) = -3y.
  2. Use Tn=a+(n−1)dT_n = a + (n - 1)d: Tn=5y+1+(n−1)(−3y)T_n = 5y + 1 + (n - 1)(-3y).
  3. Expand: 5y+1−3ny+3y=8y−3ny+15y + 1 - 3ny + 3y = 8y - 3ny + 1.
  4. So Tn=(8−3n)y+1T_n = (8 - 3n)y + 1, option C.

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