Question

the sum of first term'n 'terms of an AP is given by the formula sn =3n square +n then its 3rd term is​

Answer 1

Answer:

sn=3n^2+n

s1=3.1^2+1=3+1=4

so 1st term=4

s2=3.2^2+2=3.4+2=12+2=14

2nd term=14-4=10

common difference=10-4=6

3rd term=2nd term +6=10+6=16

Answer 2

Answer:

16

Step-by-step explanation:

Sn=3n square+n

S3=3(3) square+3

= 27+3

= 30-----1

sum of three terms =30 according to equation 1

let a=1st term

a+d =2nd term---2

a+2d=3rd term---3

a+a+d+a+2d=30

3a+3d= 30(divide the equation by 1)

a+d=10

2nd term=10(by 3 and 4)

Same common difference,therefore

S(1)=3(1)square+1

=3+1

1st term=4

S(2)= 3(2)square+2

= 3(4)+2

=12+2

= 14

A3= 4+(3-1)6

= 4+2×6

= 4+12

= 16

therefore,third term= A3=16