Question

dada a PA (7,11,15,...,123), determine: a) o tero geral b)a18

Answer 1

an= a1 + (n-1).r

 

 

a)    123 = 7 +(n-1)4

 

123 = 7 + 4n - 4

123+4 -7 = 4n

 

4n = 120

 n= 120/4

 

n= 30

 

 

b) a18= 7 +(18-1).4

 

  a18= 7 + 17.4

 

a18= 7 + 68

 

a18= 75