Question

Descubra o valor de x na PA (x+3,2x+2,4x+8)

Answer 1

$a1 = x+3$
$a2 = 2x+2$
$a3 = 4x+8$

$an = a1+(n-1)r$
$a3 = a1+(3-1)r$
$a3 = a1+2r$

$r = a2-a1$
$r = (2x+2) - (x+3)$
$r = 2x +2 - x - 3$
$r = x - 1$

$a3 = a1+2r$
$4x+8 = x + 3 +2(x-1)$
$4x+8 = x + 3 +2x-2$
$4x+8 = 3x + 1$
$4x - 3x = 1 - 8$
$x = -7$

$P.A.(-4,-12,-20)$
$r = -8$

Answer 2

a2 - a1 = a3 - a2

===

a1 = x + 3
a2 = 2x + 2
a3 = 4x + 8

===

(2x + 2) - (x + 3 = (4x +8) - (2x + 2)
2x + 2  -x - 3 = 4x + 8 - 2x - 2
2x - x + 2 - 3 = 4x - 2x + 8 - 2
x - 1 = 2x + 6
x - 2x = 6 + 1
-x = 7 . (-1)
x = -7