Q9 of 178 Page 548

What is the sum of first n terms of the AP a, 3a, 5a, ....

Here, first term = a

Common difference = 3a - a = 2a

Now, Sum of first n terms of an AP is given by:

S_n = [2a + (n - 1)d]

where a is the first term and d is the common difference.

∴ Sum of first n terms of given AP is given by:

S_n = [2a + (n - 1)2a]

= [2a + 2an - 2a]

= [2an]

= n²a

How many three - digit natural numbers are divisible by 9?

If the sum of first m terms of an AP is (2m² + 3m) then what is its second term?

What is the 5th term from the end of the AP 2, 7, 12, ..., 47?

If a_n denotes the nth term of the AP 2, 7, 12, 17, ..., find the value of (a₃₀ – a₂₀).