The sum of first n terms of an ap is 3n2+4n.find the 25th term
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Answer:
Sₙ = 3n² + 4n
First term (a₁) = S₁ = 3(1)² + 4(1) = 7
S₂ = a₁ + a₂ = 3(2)² + 4(2) = 20
a₂ = 20 - a₁ = 20 - 7 = 13
So, common difference (d) = a₂ - a₁ = 13 - 7 = 6
Now, aₙ = a + (n - 1)d
a₂₅ = 7 + (25 - 1) 6
= 7 + 24 6
= 7 + 144
= 151
FOLLOW MEH!
Explanation:
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