Answers

  • Brainly User
2016-07-03T21:45:37+08:00
General formula:  an = a₁ + (n-1)(d)

Step 1: Find the difference using the given term a₂ = 15.
a₁₅ = a₁ + (n-1) (d)
15 = a₁ + (2-1) (d)
15 = a₁ + 1d
a₁ = d - 15

a₉=39
39 = d-15 + (9-1) (d)
39 = d-15 + 8d
39 = 9d - 15
9d = 39 + 15
9d/9 = 54/9
d = 6

Step 3:  Find a₁.
a₁ = ?
d = 6
a₂ = 15

15 = a₁ + (2-1) (6)
15 = a₁ + 6
a₁ = 15-6
a₁ = 9

Step 3:  Find a₁₆.
a₁₆ = 9 + (16-1)(6)
a₁₆ = 9 + (15)(6)
a₁₆ = 9 + 90
a₁₆ = 99

ANSWER:  a₁₆ = 99
 
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