Find the sum of the first 15 terms of each of the following sequences having n^th term as

Question

Find the sum of the first 15 terms of each of the following sequences having n th term as (i) (ii) (iii) (iv)

Philoid · Accepted Answer

(i)

Put n = 1

a₁ = 3 + 4(1) = 7

Put n = 15

a₁₅ = 3 + 4(15) = 63 = l

Sum of 15 terms, S₁₅ = [a + l]

= [7 + 63] = 525

Put n = 1

b₁ = 5 + 2(1) = 7

Put n = 15

b₁₅ = 5 + 2(15) = 35 = l

Sum of 15 terms, S₁₅= [a + l]

= [7 + 35] = 315

Put n = 1

x₁ = 6 – 1 = 5

Put n = 15

x₁₅ = 6 – 15 = -9

Sum of 15 terms, S₁₅= [a + l]

= [5 - 9] = -30

Put n = 1

y₁= 9 – 5(1) = 4

Put n = 15

y₁₅= 9 – 5(15) = -66

Sum of 15 terms, S₁₅= [a + l]

= [4 - 66] = -465