Respostas

2014-03-29T08:01:56-03:00
An = a1 + (n - 1) x r
an = 3 + (12 - 1) x 2
an = 3 + 11 x 2
an = 3 + 22
an = 25

PA (3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25,..)
9 3 9
2014-03-29T08:15:20-03:00

  AN = a1+ ( n-1).r
  a1= primeiro termo =3
  r= razão=7-5=2
a10= 
substituindo na fórmula
AN = a1+ ( n-1).r
 a12= 3 + (12-1) .2
a12=  3+11 .2
 a12= 3+22=25
a12=25
 pa=(3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37...)
3 3 3