If a minus sign is in front of the bracket, you call it a minus bracket.
You can think of a (-1) in front of the bracket instead of the minus sign. Each member within the bracket is then multiplied by (-1).
If you expand or factorize a minus bracket, the signs change from all factors.
$-(a+b)=(-1)\cdot (a+b)= -a-b$
$=(-1)\cdot 8x+(-1)\cdot (-2)$
- $-5x+18z$ $=-(5x-18z)$