The 5th term of an AP is – 3 and its common difference is – 4. The sum of its first 10 terms is

Question

Philoid · Accepted Answer

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

Given: a₅ = - 3

Common difference = d = - 4

Now, Consider a₅ = - 3

⇒ a + 4d = - 3

⇒ a + 4(-4) = - 3

⇒ a - 16 = - 3

⇒ a = 16 - 3

⇒ a = 13

Now, Sum of first n terms of an AP is

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

∴ Sum of first 10 terms is given by:

S₁₀ = [2(13) + (10 - 1)(-4)]

= 5[26 - 36]

= 5 × (-10)

= - 50