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puteri [66]
3 years ago
13

8 times of the eight term of an arithmetic progression is equal to 12 times of the twelfth term. find its first term if the comm

on difference is -2 .​
Mathematics
1 answer:
Ilya [14]3 years ago
6 0

Answer:

a₁ = 38

Step-by-step explanation:

Given AP, where:

  • 8a₈ = 12a₁₂
  • d = -2,
  • a₁ = ?

=============

<h3>Solution</h3>

aₙ = a₁ + (n-1)d

  • a₈ = a₁ + 7d = a₁ + 7*(-2) = a₁ - 14
  • a₁₂ = a₁ + 11d = a₁ + 11*(-2) = a₁ - 22

8a₈ = 12a₁₂

  • 8(a₁ - 14) = 12(a₁ - 22)
  • 2(a₁ - 14) = 3(a₁ - 22)
  • 2a₁ - 28 = 3a₁ - 66
  • 3a₁ - 2a₁ = -28 + 66
  • a₁ = 38
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