Question

o sétimo termo da p.a na qual a4= 25 e r= -5

 

Answer 1

$a_{n} = a_{1} + (n - 1)r$
$a_{4} = a_{1} + (4 - 1)r$
$a_{4} = a_{1} + 3r$
$25 = a_{1} + 3(-5)$
$25=a_{1}-15$
$25+15=a_{1}$
$40=a_{1}$

$a_{n} = a_{1} + (n - 1)r$
$a_{7} = a_{1} + (7 - 1)r$
$a_{7} = a_{1} + 6r$
$a_{7} = 40 + 6(-5)$
$a_{7} = 40 - 30$
$a_{7} = 10$