Distributing a Minus

When the number outside is negative, its sign is multiplied into every term too. $-2\left(x-5\right)$: -2 times x is -2x, and -2 times -5 is +10, because a negative times a negative is positive. So the result is $-2x+10$.

A minus sign alone in front of parentheses is a hidden -1. $-\left(x+3\right)$ means $-1 \cdot \left(x+3\right)$, which is $-x-3$. Every sign inside flips: the plus in front of 3 becomes a minus.

The usual slip is to change only the first sign and write -2x - 10. Treat each term inside as a signed number, multiply it by the outside number, and use the sign rules from Section 1 every time.