Answer:
3x^4 + 7x^3 - 5x^2 + 8x - 13
Explanation:
(3x^4 + 7x^3 - 9) - (5x^2 - 8x + 4) =
The negative sign to the left of the second set of parentheses changes every sign inside the parentheses.
The first set of parentheses is unnecessary, so we just drop it.
= 3x^4 + 7x^3 - 9 - 5x^2 + 8x - 4
Now we combine like terms.
= 3x^4 + 7x^3 - 5x^2 + 8x - 13