Question

Find the sum of 21 terms of ap -30,-27-24

Answer 1

Step-by-step explanation:

it is 0. qwertyuiopdhxhdfuhcfj

Answer 2

Sum of first 21 terms of given AP is zero.

Given:

• An A.P.
• -30, -27, -24,...

To find:

• Find the sum of 21 terms of AP.

Solution:

Formula/ Concept to be used:

Sum of n terms of AP:

$\bf S_n = \frac{n}{2} (2a + (n - 1)d)$

here,

a: first term

d: Common difference

n: number of terms.

Step 1:

Write the terms used in formula.

Here,

First term(a)= -30

Common difference(d)=3

Number of terms(n)=21

Step 2:

Find the sum of first 21 terms.

Put the values in the formula.

$S_{21} = \frac{21}{2} [2 \times ( - 30) + (21 - 1)3]$

or

$S_{21} = \frac{21}{2} ( - 60 + 60)$

or

$S_{21} = \frac{21}{2} (0)$

or

$\bf S_{21} = 0$

Thus,

Sum of first 21 terms of given AP is zero.

Learn more:

1) If the sum of first 9 terms of an AP is equal to the sum of its first 11 terms, then find the sum of its first 20 terms.

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2) If the sum of the first 8 terms of AP is 136 and that of first 15 terms is 465 then find the sum of first 25 terms

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