Question

determine o vigésimo da PA (2,5,8)

Answer 1

a1 = 2
r = 3
a20 = ?
formula = an = a1+ (n-1).r

a20= 2+(20-1).3
a20= 2+19.3
a20= 2+57
a20=59
entao sera 59 

Answer 2

an= 20  
a1= 2
r=3

an= a1+ (n-1) . r 

a20= 2 + (20 -1) . 3
a20= 2 + 19 . 3
a20= 2 + 57
a20= 59