The Minus Reaches Everything

The same rule works when there are more terms inside the parentheses. In 2x^2 - (x^2 - 4x + 1), a trinomial is being subtracted, so all three of its terms change sign: 2x^2 - x^2 + 4x - 1.

Do not forget the last term. The constant 1 at the end is inside the parentheses too, so it changes to -1. Count the terms inside before you start, and then check that you changed that many signs.

Collect the like terms that remain. The squared terms give 2x^2 - x^2 = x^2. The 4x and the -1 have no like terms, so they stay as they are. The result is x^2 + 4x - 1.