Question

Calcule a razão e o vigésimo quinto termo da PA(-16,-18,-20,...).​

Answer 1

$PA\,(-16,-18,-20,\dotsc)$

$r=a_2-a_1$

$r=-18-(-16)$

$r=-18+16$

$\boxed{\boxed{r=-2 }}$

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

$a_{25}=-16+(25-1)\cdot(-2)$

$a_{25}=-16+(24)\cdot(-2)$

$a_{25}=-16-48$

$\boxed{\boxed{ a_{25}= -64}}$