Question

determine o 20° termo da PA (3,9,15,...)

Answer 1

P.A.(3,9,15,...)
r = a 2 - a 1
r = 9 - 3
r = 6
a 20 = a 1 + (n - 1 ).r
a 20 = 3 + (20 - 1 ). 6
a 20 = 3 + 19.6
a 20 = 3 + 114
a 20 = 117

Answer 2

an = a1 + (n - 1) r
a20 = 3 + (20 - 1) 6
a20 = 3 + (19.6)
a20 = 3 + 114 = 117