Bài 1) Phân tích các đa thức sau thành nhân tử:
a) xy + 3x - 7y - 21
b) 2xy - 15 - 6x +5y
c) 2x2 y + 2xy2 - 2x - 2y
d) x2 - (a+b)x + ab
e) 7x3y - 3xyz - 21x2 + 9z
f) 4x + 4y - x2(x+y)
g) y2 + y - x2 + x
h) 4x2 - 2x - y2 - y
i) 9x2 - 25y2 - 6x + 10y
j) x(x+3) - 5x(x-5) - 5(x+3)
k) (5x-4)(4x-5) - (x-3)(x-2) - (5x-4)(3x-2)
l) (5x-4)(4x-5) + (5x-1)(x+4) + 3(3x-2)(4-5x)
m) (5x - 4)2 + (16-25x2) + (5x-4)(3x+2)