Question

find this is the given a=7;a13=35 and find down and S13
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Answer 1

Hiii dude....

a=7

a13=35

It's means no.of term is 35.

So, n=13

We know that,

aⁿ=a+(n-1)d

35=7+(13-1)d

35=7+12d

35-7=12d

28=12d

12d=28

d=28/12

d=7/3

Now,

$s13 = \frac{13}{2} {2 \times 7 + (13 - 1) \times \frac{7}{3} }$

........................ By Sⁿ formula

=13/2{14+28}

=13/2×42

=13×21

=273

Hence,

d=7/3 and s13=273.

Answer 2

Solution:

a=7

a13=35

It's means no.of term is 35.

So, n=13

We know that,

aⁿ=a+(n-1)d

35=7+(13-1)d

35=7+12d

35-7=12d

28=12d

12d=28

d=28/12

d=7/3

Then,

s13= 2/13 ×2×7+(13−1)× 3/7

By Using Sⁿ formula

=13/2{14+28}

=13/2×42

=13×21

=273

Hence,

d=7/3 and s13=273.