Question

Fie progresia aritmetica in care a3=5 si a6=11. Calculati a9 . URGENT VA ROG

Answer 1

a3=5 => 2x3-1=5
a6=11 => 2x6-1=11
a9=17 <=> 2x9-1=17

Answer 2

Stim ca :a3=5
a6=11
a9=?
$\left \{ {{a_{1}+2r=5|*(-1)} \atop {a_{1}+5r=11}} \right. \ \textless \ =\ \textgreater \ -2r+5r= -5+11\ \textless \ =\ \textgreater \ 3r=6 |:3 =\ \textgreater \ r=2$
Aflam a1:
a1+2r=5
a1+4=5=>a1=1
Deci:$a9=a1+8r=\ \textgreater \ a9=1+8*2=1+16=17=\ \textgreater \ a9=17$