Answer: This is a property of addition in mathematics called the associative property. To prove that (A+B) + C = A + (B+C), we can demonstrate that both expressions have the same value. Starting with the left-hand side: (A+B) + C = A + (B+C)Applying the associative property by rearranging the parentheses on the left-hand side: A + (B+C) = A + (B+C)Therefore, (A+B) + C = A + (B+C) is true and proven.