Question

If the $9^{\text{th}}$ term of an AP is 15 and the common difference is 2, then the $1^{\text{st}}$ term of the AP is .

• A. 1
• B. 0.0
• C. -1
• D. 2

Answer 1

The correct option is C -1

The $n^{\text{th}}$ term of an AP with first term $a$ and common difference $d$ is given by
$a_n=a+(n-1)d.$
Given that $a_9=15$ and $d=2.$
$a+(9-1)2=15$
$a+16=15$
$a=-1$
Thus, the first term of the AP is -1.