Question

In the series 3,9,15,....What will be the 21st term?

Answer 1

Answer:

We can judge that it is A.P.

With 6 as difference

nth term in A.P. = a+(n-1)d

a= 3, n = 21, d = 6

So, 21st term will be = 3+(20)6 = 123

Answer 2

Step-by-step explanation:

hey mate this is in arthemetic progression

to find difference : a2 - a1 = 9 - 3 =6

first term is called = a = 3

an = a + ( n - 1 ) × d

= 3 + ( 20 - 1 ) × 6

= 3 + ( 20 ) × 6

= 3 + 120

= 123