Question

if the nth term of an AP is (2n-1) , then find sum of its first three terms

Answer 1

An=(2n-1),

then
A1=(2×1-1)=1=first term(a),

A2=(2×2-1)=3,

A3=(2×3-1)=5,

then

d=3-1=2,


therefore

Sum of first three terms=1+3+5=9

Answer 2

Answer:

Step-by-step explanation:

an= 2n-1 if n=1 awill be equal to 1 if n=2 second term=3 d=2 therefore substituting values in formula we get sum of three terms as 9