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Answer:
a₁₅ = 30
Step-by-step explanation:
The nth term of an arithmetic sequence is
= a₁ + (n - 1)d
where a₁ is the first term and d the common difference
Given a₅ = 10 and a₁₀ = 20 , then
a₁ + 4d = 10 → (1)
a₁ + 9d = 20 → (2)
Subtract (1) from (2) term by term to eliminate a₁
5d = 10 ( divide both sides by 5 )
d = 2
Substitute d = 2 into (1) and solve for a₁
a₁ + 4(2) = 10
a₁ + 8 = 10 ( subtract 8 from both sides )
a₁ = 2
Then
a₁₅ = 2 + (14 × 2) = 2 + 28 = 30