It is known that the sum of the first n terms of the arithmetic sequence {an} is Sn, S15 > 0, S16

It is known that the sum of the first n terms of the arithmetic sequence {an} is Sn, S15 > 0, S16

Sn = n (a1 + an) / 2, so S15 = 15a8 > 0, a8 > 0
S16=8(a1+a16)=8(a8+a9)