Question

The sum of the first n terms of an AP is (3n^2-4n).Find its 1.nth term,2.first term and 3.common difference?(please answer with complete process)

Answer 1

Answer:

n term is 6n-7, first term is 4 , common difference is 5

Step-by-step explanation:

Sn=3n^2-4n

S(n-1)=3(n-1)^2-4(n-1)

an=Sn-S(n-1)

=3n^2-4n-(3(n-1)^2-4(n-1)

=3n^2-4n-3(n-1)^2+4(n-1)

=3n^2-3(n-1)^2+4(n-1)-4n

=3(n^2-(n-1)^2)+4(n-1-n)

=3(n-n+1)(n+n-1)+4(-1)

=3(2n-1)-4

=6n-3-4

=6n-7

Sn=3n^2-4n

At n=1

S1=3(1)^2+1

S1=3+1

S1=4

a1=4

At n=2

S2=3(2)^2+1

=3(4)+1

=12+1

=13

a1+a2=13(S2=a1+a2)

4+a2=13

a2=13-4

a2=9

d=a2-a1

=9-4

=5

Answer 2

Answer:

Step-by-step explanation: