When the plus sign comes before the brackets, the brackets are removed and the formula in the brackets remains the same.

When the minus sign comes before the parentheses, remove the parentheses, and the plus sign in the parentheses becomes a minus sign, and the minus sign becomes a plus sign.

The basis of the law is actually the law of multiplication and distribution. Note: Pay attention to the symbol before brackets, which is the basis for whether the items in brackets change their symbols after removing brackets.

When deleting brackets, the symbol before brackets should be deleted together with brackets.

It should be noted that when there is a "-"sign in front of the brackets, the symbols of the items in brackets will change after the brackets are removed. You can't just change the symbol of the first item or the first few items in brackets and forget to change other symbols.

If there is a numerical factor in front of the brackets, before removing the brackets, multiply the number with the items in brackets by multiplication and division to avoid mistakes.

When you encounter multiple layers of brackets, you usually remove the brackets from inside to outside, and you can also count the number of "-"from outside to inside.