Step-by-step explanation:
I think the expression is
(4x² + 9x - 7) - (-7x² + 5x - 1)
and that is the same as
4x² + 9x - 7 + 7x² - 5x + 1 =
= 11x² + 4x - 6
remember that the combination of two '-' signs turns this into one '+' sign.
to subtract a negative number is indeed the same as adding a positive number with the same absolute value.
