(Q12).Find the sum of the following APs:
(i) 2, 7, 12,…, to 10 terms.
Given A.P: 2, 7, 12, …… to 10 terms
a =
; d = a2 – a1 =
–
=
; n =
S
n
=
n
2
[2a + (n-1)d]
∴ S
10
=
2
[2 ×
+ (
-1)
]
=
[
+
×
]
=
[
+
]
=
×
=
Clear