Question

First term of an arithmetic sequence is 28 and the
common difference is -4.
(a) Write the arithmetic sequence.
(b) Find its 8th term
(c) What is the sum of its first 15 terms?
(d) What is the sum of the first 15 terms of the
arithmetic sequence -28, -24.-20, .....​

Answer 1

Answer:

a = 28 and d = - 4

(a) The arithmetic sequence is,

28, 24, 20, 16, 12, 8, 4, 0, -4, ....

(b) The 8th term

= a + 7d

= 28 - 7*4

= 28 - 28 = 0

(c) sum of first 15 terms

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

= 15/2*(2*28 + 14*(-4))

= 15/2*(56 - 56) = 0

(d) sum of the first 15 terms of the arithmetic sequence -28, -24, -20, .....

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

= 15/2*(-2*28 + 14*(4))

= 15/2*(-56 + 56) = 0