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)
a,\(xy+3x-7y-21\)
\(=x\left(y+3\right)-7\left(y+3\right)\)
\(=\left(y+3\right)\left(x-7\right)\)
\(b,2xy-15-6x+5y\)
\(=\left(2xy-6x\right)+\left(-15+5y\right)\)
\(=2x\left(y-3\right)-5\left(3-y\right)\)
\(=2x\left(y-3\right)+5\left(y-3\right)\)
\(=\left(y-3\right)\left(2x+5\right)\)
\(c,2x^2y+2xy^2-2x-2y\)
\(=2\left(x+1\right)\left(xy-1\right)\)
\(d,x^2-\left(a+b\right)x+ab\)
\(=\left(a-x\right)\left(b-x\right)\)
\(e,7x^3y-3xyz-21x^2+9z^2\)
\(=\left(xy-3\right)\left(7x^2-3z\right)\)
\(f,4x+4y-x^2\left(x+y\right)\)
\(=-\left(x-2\right)\left(x+2\right)\left(x+y\right)\)
\(g,y^2+y-x^2+x\)
\(=-\left(x-y-1\right)\left(x+y\right)\)
\(h,4x^2-2x-y^2-y\)
\(=\left(2x-y-1\right)\left(2x+y\right)\)
\(i,9x^2-25y^2-6x+10y\)
\(=\left(2x-y-1\right)\left(2x+y\right)\)
\(j,x\left(x+3\right)-5\left(x-5\right)-5\left(x+3\right)\)
\(=\left(3-4x\right)\left(x-5\right)\)
\(k,\left(5x-4\right)\left(4x-5\right)-\left(x-3\right)\left(x-2\right)-\left(5x-4\right)\left(3x-2\right)\)
\(=2\left(2x-1\right)\left(x-3\right)\)
\(l,\left(5x-4\right)\left(4x-5\right)-\left(x-3\right)\left(x-2\right)-\left(5x-4\right)\left(3x-2\right)\)
\(=-4\left(5x-1\right)\left(x-2\right)\)
\(m,\left(5x-4\right)^2+16-25x^2+\left(5x-4\right)\left(3x+2\right)\)
\(=3\left(x-2\right)\left(5x+4\right)\)
