Question

Find the sum to n terms of the series.
1.3 + 4.5+ 7.7 +10.9 + ...​

Answer 1

Step-by-step explanation:

13.11 is the missing answer of this question

Answer 2

The sum to n terms of the series 1.3 + 4.5 + 7.7 + 10.9 +... is 1.6n² - 0.3n

Given,

A series:  1.3 + 4.5 + 7.7 + 10.9 +....

To Find,

The sum to n terms of the series.

Solutions,

We know that, Sₙ = n/2 [2a + (n - 1)d]

where, Sₙ is sum to n terms, n is number of terms, a is first term, and d is common difference.

Here,

a = 1.3, d = 4.5 - 1.3 = 7.7 - 4.5 = 3.2

⇒ Sₙ = n/2 [2(1.3) + (n - 1)(3.2)]

        = n/2 [2.6 + 3.2n - 3.2]

        = n/2 [3.2n - 0.6]

        = n/2(3.2n) - n/2(0.6)

        = 1.6n² - 0.3n

Hence, the sum to n terms is 1.6n² - 0.3n

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