Answer:
- (x - 3y)(3x + y)
Explanation:
Given
(x + 2y)² - (2x - y)² ← expand both parenthesis using FOIL
= x² + 4xy + 4y² - (4x² - 4xy + y²) ← distribute
= x² + 4xy + 4y² - 4x² + 4xy - y² ← collect like terms
= - 3x² + 8xy + 3y² ← factor out - 1 from each term
= - 1(3x² - 8xy - 3y²) ← factor the quadratic
Consider the factors of the product of the coefficient of the x² term and the coefficient of the y² term which sum to give the coefficient of the xy- term.
product = 3 × - 3 = - 9 and sum = - 8
The factors are - 9 and + 1
Use these factors to split the xy- term
3x² - 9xy + xy - 3y² ( factor the first/second and third/fourth terms )
= 3x(x - 3y) + y(x - 3y) ← factor out (x - 3y) from each term
= (x - 3y)(3x + y)
Thus
(x + 2y)² - (2x - y)² = - (x - 3y)(3x + y)