The sum of n natural numbers is 5n 2 + 4n. Find its 8 th term.

Here T stands for term. S n = 5n 2 + 4n S 1 = Sum of first natural number = T 1 = 5(1) 2 + 4(1) = 5 + 4 = 9. S 2 = 5(2) 2 + 4(2) = 20 + 8 = 28. T 2 = S 2 - S 1 = 28 - 9 = 19. We know that, ⇒ T 2 = a + d ⇒ 19 = 9 + d ⇒ d = 10. T 8 = a + (8 - 1)d = 9 + 7(10) = 79. Hence, 8 th term = 79.

Mathematics

The sum of n natural numbers is 5n² + 4n. Find its 8^th term.

AP

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Answer

Here T stands for term.

S_n = 5n² + 4n

S₁ = Sum of first natural number = T₁

= 5(1)² + 4(1) = 5 + 4 = 9.

S₂ = 5(2)² + 4(2) = 20 + 8 = 28.

T₂ = S₂ - S₁ = 28 - 9 = 19.

We know that,

⇒ T₂ = a + d

⇒ 19 = 9 + d

⇒ d = 10.

T₈ = a + (8 - 1)d = 9 + 7(10) = 79.

Hence, 8^th term = 79.

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The sum of n natural numbers is 5n² + 4n. Find its 8^th term.

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