Question

If the 10th term of an ap is 47 and its first term is 2 find the sum of its 15th term

Answer 1

Answer:

Step-by-step explanation:

Solution :-

Let a be the first term and d be the common difference of the AP.

Here a = 2, a₁₀ = 47

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

⇒ a₁₀ = a + 9d

⇒ 47 = 2 + 9d

⇒ 45 = 9d

⇒ d = 45/9

⇒ d = 5

Now, a = 2, d = 5, n = 15

S(n) = n/2(2a + (n - 1)d)

⇒ S(n) = 15/2(2 × 2 + (15 - 1)5)

⇒ S(n) = 15/2(4 + 70)

⇒ S(n) = 15/2 × 74

⇒ S(n) = 555

Hence, the sum of its 15th term is 555.