中三數學 (急)

3x² + 5xy - 2y² + x + 9y - 4= 3x² + (5y+1)x - (2y² - 9y + 4)= 3x² + (5y+1)x - (2y - 1)(y - 4)
3x.......... - (y - 4)
........X
..x............ (2y-1)
________________________________(3x)(2y-1) - x(y-4) = 5xy + x = (5y+1)x
So 3x² + 5xy - 2y² + x + 9y - 4= (3x - (y - 4)) (x + 2y-1)= (3x - y + 4) (x + 2y - 1)
Alternatively :3x² + 5xy - 2y² + x + 9y - 4= (3x - y)(x + 2y) + x + 9y - 4= (3x - y)(x + 2y) + 4(x + 2y) - (3x - y) - 4= (3x - y + 4)(x + 2y) - (3x - y + 4)= (3x - y + 4) (x + 2y - 1)

This question is from a secondary 3's Mathematic book

1) Excellent answer for ☂雨後陽光☀!

2) I wonder who will give such a difficult question to a S.3 student. I highly suspect even it appears in HKDSE, over 75 % candidates cannot answer.