Question

find the sum of first 20 terms of 4,8,12,16,20,24,28....​

Answer 1

Answer:

Your input 0,4,8,12,16,20,24,28 appears to be an arithmetic sequence ... the number n of terms being added (here 8), multiplying by the sum of the first and last number in the progression (here 0 ...

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Answer 2

Given:

To find the sum of first 20 terms of 4,8,12,16,20,24,28....​

Solution:

Know that the sum of the first $n$ natural numbers id given by

$\[ = \frac{{n\left( {n + 1} \right)}}{2}\]$

Therefore,

$\[ = 4 + 8 + 12 + 16 +20+ 24 + 28 + {----20^{th}}{\rm{term}}\]$

Now, take 4 as common,

$\[ = 4\left( {1 + 2 + 3 + 4 + 5 + 6 + {{----20}^{th}}{\rm{term}}} \right)\]$

$\[\begin{array}{l} = 4 \times \frac{{20\left( {20 + 1} \right)}}{2}\\ = 4 \times 210\\ = 840\end{array}\]$

Hence the sum the first 20 terms of 4,8,12,16,20,24,28....​ is 840.