Question

dada as progressões (5, 8, 11...) determine o 21° termo

Answer 1

$(5,8,11,\dots)$

$a_1=5 \ \ \ \ \ \ \ \ \ \ r=8-5 \iff r=3$

$a_n=a_1+(n-1)\cdot r$

$a_{21}=a_1+20r$

$a_{21}=5+20\cdot3$

$a_{21}=5+60 \iff \boxed{a_{21}=65}$