인수 분해: - 4 (x - 2y) 2 + 9 (x + y) 2.

인수 분해: - 4 (x - 2y) 2 + 9 (x + y) 2.

- 4 (x - 2y) 2 + 9 (x + y) 2, = [3 (x + y)] 2 - [2 (x - 2y)] 2, = (3x + 3y + 2x - 4y) (3x + 3y - 2x + 4y), = (5x - y) (x + 7 y).