When you simplify the expression (3x³ - 2y² + 5x²) - (3x³ - 2y² + 5x²), you are essentially subtracting the second set of parentheses from the first set of parentheses.
The terms 3x³ and -3x³ cancel out because they have the same coefficient and opposite signs. The terms -2y² and -(-2y²) simplify to 0, or simply disappear, because subtracting a negative is the same as adding a positive. Similarly, the terms 5x² and -5x² cancel out.
So, after simplifying the expression, you are left with:
(3x³ - 2y² + 5x²) - (3x³ - 2y² + 5x²) = 0
In other words, the expression simplifies to zero or the additive identity, indicating that there is no net change when you subtract the two sets of parentheses.