Question

quantos termos tem a pa 5,8,11.. 23

Answer 1

an = a1 + ( n - 1 ) . r
23 = 5 + ( n - 1 ) . 3
23 = 5 + 3n - 3 
23 = 3n +2
3n = 23 - 2 
3n = 21
n = 21/3
n = 7 termos     ok