Find the sum of first n odd numbers.
Last updated date: 20th Mar 2023
•
Total views: 309k
•
Views today: 3.87k
Answer
309k+ views
Hint- The formula for the sum of an A.P is${{\text{S}}_n} = \dfrac{n}{2}\left( {2{a_1} + \left( {n - 1} \right)d} \right)$, where n is number of terms.
We have to find out the sum of first n odd numbers.
$ \Rightarrow 1 + 3 + 5 + 7 + .........................n{\text{ terms}}{\text{.}}$
As we see that $\left( {1,3,5,7..............n} \right)$makes an A.P
Where, number of terms of the series${\text{ = n}}$
First term $\left( {{a_1}} \right) = 1$
Common difference$\left( d \right) = \left( {3 - 1} \right) = \left( {5 - 3} \right) = 2$
Now apply the formula of sum of an A.P
$
{{\text{S}}_n} = \dfrac{n}{2}\left( {2{a_1} + \left( {n - 1} \right)d} \right) \\
\Rightarrow {{\text{S}}_n} = \dfrac{n}{2}\left( {2 \times 1 + \left( {n - 1} \right)2} \right) \\
\Rightarrow {{\text{S}}_n} = \dfrac{n}{2}\left( {2 + \left( {n - 1} \right)2} \right) = n\left( {1 + n - 1} \right) = {n^2} \\
$
Note- In such types of questions always remember the basic formulas of an A.P which is stated above, then from the given condition calculate the values of first term and common difference, then apply the formula of sum of an A.P we will get the required sum of first n odd numbers.
We have to find out the sum of first n odd numbers.
$ \Rightarrow 1 + 3 + 5 + 7 + .........................n{\text{ terms}}{\text{.}}$
As we see that $\left( {1,3,5,7..............n} \right)$makes an A.P
Where, number of terms of the series${\text{ = n}}$
First term $\left( {{a_1}} \right) = 1$
Common difference$\left( d \right) = \left( {3 - 1} \right) = \left( {5 - 3} \right) = 2$
Now apply the formula of sum of an A.P
$
{{\text{S}}_n} = \dfrac{n}{2}\left( {2{a_1} + \left( {n - 1} \right)d} \right) \\
\Rightarrow {{\text{S}}_n} = \dfrac{n}{2}\left( {2 \times 1 + \left( {n - 1} \right)2} \right) \\
\Rightarrow {{\text{S}}_n} = \dfrac{n}{2}\left( {2 + \left( {n - 1} \right)2} \right) = n\left( {1 + n - 1} \right) = {n^2} \\
$
Note- In such types of questions always remember the basic formulas of an A.P which is stated above, then from the given condition calculate the values of first term and common difference, then apply the formula of sum of an A.P we will get the required sum of first n odd numbers.
Recently Updated Pages
Calculate the entropy change involved in the conversion class 11 chemistry JEE_Main

The law formulated by Dr Nernst is A First law of thermodynamics class 11 chemistry JEE_Main

For the reaction at rm0rm0rmC and normal pressure A class 11 chemistry JEE_Main

An engine operating between rm15rm0rm0rmCand rm2rm5rm0rmC class 11 chemistry JEE_Main

For the reaction rm2Clg to rmCrmlrm2rmg the signs of class 11 chemistry JEE_Main

The enthalpy change for the transition of liquid water class 11 chemistry JEE_Main

Trending doubts
Difference Between Plant Cell and Animal Cell

Write an application to the principal requesting five class 10 english CBSE

Ray optics is valid when characteristic dimensions class 12 physics CBSE

Give 10 examples for herbs , shrubs , climbers , creepers

Write the 6 fundamental rights of India and explain in detail

Write a letter to the principal requesting him to grant class 10 english CBSE

List out three methods of soil conservation

Fill in the blanks A 1 lakh ten thousand B 1 million class 9 maths CBSE

Write a letter to the Principal of your school to plead class 10 english CBSE
