Why the location of the parentheses can affect the value of the expression?

Answer 1

the parenthesis take precedence in the order of operations. The operations inside the parenthesis are taken first.

Example

6 - 2 + 3 without parenthesis, you take addition/subtraction in order from left to right.

6 -2 = 4, then add 3 = 7

Now add some parenthesis.

(6 - 2) + 3 Note that we do the (6-2) first because it's in parentheses, then add 3

(4) + 3 = 7

6 - (2 + 3). Now perform (2+3) first = 5, then 6 - (5) = 1.