Question

for an A.P if t1=4,tn=40, and n=13 find Sn​

Answer 1

$\sf\red{\underline{\underline{Answer:}}}$

$\sf{The \ value \ of \ Sn \ is \ 286.}$

$\sf\orange{Given:}$

$\sf{In \ an \ A.P.}$

$\sf{\implies{t1=4}}$

$\sf{\implies{tn=40}}$

$\sf{\implies{n=13}}$

$\sf\pink{To \ find:}$

$\sf{The \ value \ of \ Sn}$

$\sf\green{\underline{\underline{Solution:}}}$

$\boxed{\sf{Sn=\frac{n}{2}[t1+tn]}}$

$\sf{S13=\frac{13}{2}[4+40]}$

$\sf{S13=\frac{13}{2}\times44}$

$\sf{S13=13\times22}$

$\sf{S13=286}$

$\sf\purple{\tt{\therefore{The \ value \ of \ Sn \ is \ 286.}}}$

$\sf\blue{Extra \ information}$

$\sf{tn=a+(n-1)d}$

$\sf{Sn=\frac{n}{2}[2a+(n-1)d]}$

$\sf{2\times \ t2=t1+t3}$

Answer 2

Sum=286 hope it will useful to you