Answers

  • Brainly User
2016-06-20T20:15:14+08:00
To find the common difference (d):  a₉ - a₈   ⇒  60 - 54 = 6

a₁ = ?    d = 6      a₉ = 60

an = a₁ + (n-1) (d)

a₉ = a₁ + (9-1) (6)

60 = a₁ + (8) (6)

60 = a₁ + 48

a₁ = 60 - 48

a₁ = 12

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