The 18th term of A.P is 25 find its first term if its common difference is 2.

The formula for the $n$-th term ($T_n$) of an AP is given by:

$$T_n = a + (n-1)d$$

where $a$ is the first term, $n$ is the term number, and $d$ is the common difference.

We are given:

• The 8th term ($T_8$) is 25. So, $T_n = 25$ and $n = 8$.
• The common difference ($d$) is 2. So, $d = 2$. We need to find the first term ($a$).

$$25 = a + (7)2$$ $$25 = a + 14$$

Subtract 14 from both sides to find $a$:

$$a = 25 - 14$$ $$a = 11$$

The first term of the AP is 11.

$$11$$