Question

a1=3
an=39
Sn=210
r=?
nr de termeni=?

Answer 1

Sn = (a₁+an) x n /2 = 210 => n = (210x2)/(a₁+an) = 420/42 =10

n = 10 termeni

an = a₁+ r(n-1) => r = (an-a₁)/(n-1) = (39-3)/9 = 36/9 = 4

r = 4