Step-by-step explanation:
3x² + 3x - 1
should turn into x + 5.
so, let's subtract (x + 5), and the result is then what we have to add in negative version to the original expression (like with subtractions and additions if regular numbers).
3x² + 3x - 1 - x - 5 = 3x² + 2x - 6
so, we need to add -(3x² + 2x - 6) = -3x² - 2x + 6