Question

numa P.A A1=5 e A20=81 qual a razão

Answer 1

An=A1+(n-1)r
81=5+(20-1)r
81=5+19r
19r=81-5
19r=76
r=76/19
r=4

Answer 2

a1 = 5
q = ?
n = 20
an = 81

an = a1 + (n - 1)r
81 = 5 + (20 - 1)r
81 = 5 + (19)r
19r = 81 - 5
19r = 76
r = 76/19
r = 4