Question

in an AP,,,a=7,a13=35.. find (d) and S13​

Answer 1

Answer:

t13=a+12d=7+12*d

35=7+12d

35-7=12d

28=12d

28/12=d

d=7/3

S13=13/2(a+t13)

=13/2*42

=13*21

=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