Question

If $9^{th}$ term of an AP is 15 and the common difference is 2, then the first term of the AP is

• A. 1
• B. 0
• C. -1
• D. 2

Answer 1

The correct option is C

-1

Formula to find $n^{th}$ term of arithmetic progression is

$t_n=a_1+(n-1)d$

where,

'$a_1$' is the first term,

'd' is the common difference,

'n' is the no. of terms,

'$t_n$' is the $n^{th}$ term.

$t_n=a_1+(n-1)d$
Given, $d=2$, $a_9=15$ and $n=9$
$\Rightarrow a_1+(9-1)2=15$
$\Rightarrow a_1+16=15$
$a=-1$