For an A.P, first term a = 5 and common difference d = 3. The sum of first 8 terms is ___

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Solution

Sum of first n terms, s
$= \frac{n}{2} [2 a + (n - 1) d]$
$= \frac{8}{2}$ $(2 \times 5 + (8 - 1) \times 3)$
$= 4 (10 + 21)$
$= 31 \times 4$
= 124

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For an A.P, first term a = 5 and common difference d = 3. The sum of first 8 terms is ___

Sum of first n terms, s =n2[2a+(n−1)d] =82(2×5+(8−1)×3) =4(10+21) =31×4 = 124

Sum of first n terms, s
$= \frac{n}{2} [2 a + (n - 1) d]$
$= \frac{8}{2}$ $(2 \times 5 + (8 - 1) \times 3)$
$= 4 (10 + 21)$
$= 31 \times 4$
= 124