Ache o trigésimo termo da p.a (10,19/2,9,...)
PA = 10,19/2, 9,...
r = 19 / 2 - 10 = 19 / 2 - 20 / 2 = - 1 / 2
a30 = a1 + (n - 1).(-1 / 2
a30 = 10 + (30 - 1)(- 1 / 2)
= 10 + 29(- 1/ 2)
= 10 - 29 / 2
= 20 / 2 - 29 / 2
= - 9 / 2
a30 = - 9 / 2
Ok?
[tex]a_1=10\\r=-0,5\\ a_{30} =a_1+(n-1)r\\a_{30}=10+29*(-0,5) \\a_{30}=10-14,5\\a_{30}=-4,5[/tex]
