Question

if nth term of an Ap is (2n+1). what is the sum of 1 st 3 terms . ​

Answer 1

Given:-

$\sf{a_n}$=2n+1

To Find:-

We need to find sum of first three terms

Finding first three terms

Solution:-

$\sf{a_1}$=2(1)+1

$\sf\implies{2+1}$

$\sf\implies{3}$

$\sf{a_2}$=2(2)+1

$\sf\implies{4+1}$

$\sf\implies{5}$

$\sf{a_3}$=2(3)+1

$\sf\implies{6+1}$

$\sf\implies{7}$

$\sf\fbox\red{{\frac{1}{2}\:marks\:for\:finding\:a_1,a_2,a_3}}$

So,

Sum of First three terms = $\sf{a_1+a_2+a_3}$

=3+5+7

=15