(Q1).Find the sum of indicated number of terms in each of the following A.Ps.
(i) 16, 11, 6, …..; 23 terms.
Given: 16, 11, 6, …..; S
23
t
1
= a =
; t
2
=
; t
3
=
,
d = t
2
– t
1
=
–
= -
⇒ S
n
=
n
2
[2a + (n-1)d]
⇒ S
23
=
2
[2×
+ (
-1)×(-
)]
=
2
[
+ (
)×(-
)]
=
2
[
-
] =
× (-
)
2
= -
×
= -
Clear