CBSE BoardEnglish MediumSTD 11 ScienceMathsArithmetic Progressions2 Marks
Question
Find the sum of first n natural numbers.
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Answer
A.P. formed is 1, 2, 3, 4, ..., n.
Here,
$\text{a}=1$
$\text{d}=1$
$\text{l}=\text{n}$
So sum of n terms $=\text{s}_\text{n}=\frac{\text{n}}{2}[2\text{a}+(\text{n}-1)\text{d}]$
$=\frac{\text{n}}{2}[2+(\text{n}-1)1]$
$=\frac{\text{n}(\text{n}+1)}{2}$ is the sum of first n natural numbers.
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