Question

calcule a 12 da PA; (10,15,20...)

Answer 1

$\boxed{a_n=a_1+(n-1)*r}\\\\ a_1=10\\ r = 5\\\\ a_1_2 = 10+(12-1)*5\\\\ a_1_2 =10+11*5\\\\ a_1_2 = 10+55\\\\ \boxed{a_1_2=65}$

Answer 2

Primeiro - Encontramos a Razão da PA  
r = 15 - 10  
Razão = r  =  5

an =   a1 + ( n -1 ) . r
a12 =  10 + ( 12 -1 ) . 5
a12 =  10 + 11 . 5
a12 =  10 + 55
a12 =  65

PA = (10, 15, 20, 25, 3,0 35, 40, 45, 50, 55, 60, 65)