I really don't understand why $B$ is from $-4$ to infinity because
$x+1 ≤ 3$
$x ≤ 2$
and
$-3 ≤ x+1$
$-4 ≤ x$
Shouldn't it be $B = [-4, 2]$?
I really don't understand why $B$ is from $-4$ to infinity because
$x+1 ≤ 3$
$x ≤ 2$
and
$-3 ≤ x+1$
$-4 ≤ x$
Shouldn't it be $B = [-4, 2]$?
It is not. $$|x+1|\leq 3 \iff -3 \leq x+1 \leq 3 \iff -4 \leq x \leq 2,$$ so the interval is $[-4,2]$.