Question

The sum of first n terms of an arithmetic sequence is n2+4n.(a)what is its first term?

Answer 1

Step-by-step explanation:

Sn=n/2{2a+(n-1)d}

we have

Sn=6n

n/2{2a+(n-1)d} =6n

n{2a+(n-1)d} =12n

2a+(n-1)d=12

2a=12-(n-1)d

a=12-(n-1)d/2