Question

In parallel series a=7,a¹³=35 is given, find d and S¹³​

Answer 1

Answer:

a=7,a

13

=35

a

13

=a+(13−1)d

35=7+12d

28=12d

d=28/12=7/3

s

13

=

2

13

[2a+(13−1)

3

7

]

s

13

=

2

13

[14+(12)

3

7

]

s

13

=

2

13

[14+28]

s

13

=13×21

s

13

=273