Respuesta :

Subtract "this" from "that" ⇒ "that" - ("this")
12x² + 3xy - 5y² - (8x²  + 3xy + 4y²)
12x² + 3xy - 5y² + -8x² - 3xy - 4y²        Subtraction means add the opposite
Now Combine like terms:
12x² - 8x² = 4x²
3xy - 3xy = 0
-5y² - 4y² = -9y²
ANSWER: 4x² - 9y²