Question

In an A.P. sum of first $n$ terms is given by $4n^2+3n$. Then find the third term.

Answer 1

Given in an A.P. sum of first $n$ terms is given by $4n^2+3n$.

We know the third term $=$ the sum of first three terms $-$ the sum of first two terms. and it is $={4.3}^2+3.3-({4.2}^2+3.2)=4(9-4)+3=23$.