Question

** Determine o decimo segundo termo da PG ( 16,8,4...)

Answer 1

$a_{1}=16\\a_{2}=8\\\\q=a_{2}/a_{1}=8/16=1/2$

$a_{n}=a_{1}*q^{n-1}\\a_{12}=a_{1}*q^{12-1}\\a_{12}=a_{1}*q^{11}\\a_{12}=16*(1/2)^{11}\\a_{12}=16*(1/2)^{10}*(1/2)^{1}\\a_{12}=8*(1/2)^{10}\\a_{12}=8*(1/1024)\\a_{12}=1/128$

Answer 2

r =  a2/a1 =  8/16 = 1/2     a1=16      
 
an=a1=q^n-1   a12 =16 .(1/2)^12-1  =16.(1/2)^11= 16/2048=1/128