Question

given a= 7, a13= 35, find d and s13

Answer 1

a +12d =35
7 +12d =35
12d =28
d =14/6
s13 = 13/2[7+35]
s13 =13/2^42
s13 =13 ^21
s13 =273

Answer 2

Answer:

d = 7/3, Sn=273

Step-by-step explanation:

First term of an AP = a = 7

Thirteenth term of an AP = 35

a + 12d = 35 ------(1)

Substitute a in eq - (1)

a + 12d = 35

(7) + 12d = 35

12d = 35 - 7

12d = 28

d = 28/12

d = 7/3

In an AP sum of the terms = n/2 ( a + an )

= 13/2 ( 7 + 35)

= 13/2 ( 42)

= 13(21)

= 273