Question

What is the 25th term of this arithmetic sequence? 3, 9, 15, 21, 27, …

Answer 1

3, 9, 15, 21, 27,…
+6 +6  +6  +6

a(n) = a₁ + d(n - 1)
a(n) = 3 + 6(n - 1)
a(n) = 3 + 6(n) - 6(1)
a(n) = 3 + 6n - 6
a(n) = 6n + 3 - 6
a(n) = 6n - 3

  a(n) = 6n - 3
a(25) = 6(25) - 3
a(25) = 150 - 3
a(25) = 147

Answer 2

Answer:   147

Step-by-step explanation:

The given arithmetic sequence : 3, 9, 15, 21, 27, ….....................

From the above sequence, it can be seen that the first term $a= 3$

The common difference = $d=9-15=21-15=6$

We know that in arithmetic sequence, the nth term is given by :-

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

Then for, n=25, the 25th term will be :-

$a_{25}=3+6(25-1)\\\\\Rightarrow\ a_{25}=147$