Question

If $n^{th}$ of an $A.P.$ is $(2n+1)$, what is the sum of its first three terms?

Answer 1

Given

$n^{th}$ term of $AP=2n+1$

Sum of first three terms $=t_1+t_2+t_3$

$t_n=2n+1$

$t_1=2\left(1\right)+1=3$

$t_2=2\left(2\right)+1=5$

$t_3=2\left(3\right)+1=7$

$\therefore$ Sum $=t_1+t_2+t_3=3+5+7=15$