Verified answer

a_

a8=2+7(1/3)

a8=2+7/3

a8=13/3

18=2+(n-1)1/3

18=2-n/3-1/3

18-5/3=n/3

49/3=n/3

n=49

a1 = 2 = 6/3

a2 = 7/3

r = a2 - a1 = 7/3 - 6/3 = 1/3

a8 = a1 + 7r = 6/3 + 7/3 = 13/3

an = 18 = 54/3

an = a1 + (n - 1)*r

(n - 1)*r = an - a1

n - 1 = (an - a1)/r

n = (an - a1)/r + 1

n = (54/3 - 6/3)/(1/3) + 1

n = 54 - 6 + 1 = 49 termos

pronto