Answer:
2x² - 5xy - 2y²
Step-by-step explanation:
Subtract x² + xy + y² from 3x² - 4xy - y² to obtain the expression to be added
3x² - 4xy - y² - (x² + xy + y² ) ← distribute by - 1
=3x² - 4xy - y² - x² - xy - y² ← collect like terms
= 2x² - 5xy - 2y²
Thus
adding 2x² - 5xy - 2y² to x² + xy + y² gives 3x² - 4xy - y²
