Question

find the sum of first 15 multiplies of 8

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Answer 1

Hence ,960 are sum of the first 15 multiples of 8.17

Answer 2

Answer:

Solution:

The sum of the first n terms of an AP is given by Sₙ = n/2 [2a + (n - 1) d] or Sₙ = n/2 [a + l]

Here, a is the first term, d is a common difference and n is the number of terms.

The multiples of 8 are 8, 16, 24, 32, ...

These numbers are in an A.P.

Hence,

First term, a = 8

Common difference, d = 8

Number of terms, n = 15

As we know that sum of n terms is given by the formula Sₙ = n/2 [2a + (n - 1) d]

S₁₅ = 15/2 [2 × 8 + (15 - 1)8]

= 15/2 [16 + 14 × 8]

= 15/2 [16 + 112]

= 15/2 × 128

= 15 × 64

= 960