Question

The first term of an A.P.is - 3 and the 10th term is 15. Find S10​

Answer 1

See the attachments

Answer 2

Answer: 60

Step-by-step explanation:

a = -3

a₁₀ = 15

We know that :

aₙ = a + (n - 1)d

⇒ a₁₀ = a + (10 - 1)d

⇒ 15 = -3 + 9d

⇒ 18 = 9d

⇒ d = 2

We also know that :

Sₙ = 0.5 × n ( 2a + (n-1) × d )

⇒ S₁₀ = 0.5 × 10 ( 2(-3) + (10-1)(2) )

⇒ S₁₀ = 5 ( -6 + 18 )

⇒ S₁₀ = 60

Hope this answer helps.