Question

If nth term of AP is(2n+1) find sum of its first 3 terms

Answer 1

first three term of Ap is 3 5 7
then sum=3/2(3+7)=15

Answer 2

we can find ap by putting the value of term(n)
<n=1>
=2*1+1
=2+1
=3
<n=2>
=2*2+1
=4+1
=5
<n=3>
=2*3+1
=6+1
=7
ap is 3,5,7....a=3. d=2

sn=3/2<2*3+(3-1)2>
=3/2<6+2*2>
=3/2(6+4)
=3/2*10
=30/2
=15

hope was helpful & pls mark as brain list