Question

in an ap tn=3+2n find sn​

Answer 1

Answer:

tn=3+2n

t1=3+2(1)

=5

$\sf{S_{n}=\dfrac{n}{2}[t_{1}+t_{n}]}$

$\sf{S_{n}=dfrac{n}{2}[5+3+2n]}$

$\sf{=\dfrac{n}{2}[8+2n]}$

$\sf{=n[4+n]}$

$\sf{\therefore{S_{n}=4n+n^{2}}}$