Question

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

Answer 1

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

$r=a_2-a_1$

$r=-18-(-16)$

$r=-18+16$

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

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

$a_{40}=-16+(40-1)\cdot(-2)$

$a_{40}=-16+(39)\cdot(-2)$

$a_{40}=-16-78$

$\boxed{\boxed{ a_{40}= -94 }}$