7) \(x^3-3x^2-4x+12\)
\(=x^2\left(x-3\right)-4\left(x-3\right)\)
\(=\left(x-3\right)\left(x-2\right)\left(x+2\right)\)
8: \(4x^3-8x^2-9x+18\)
\(=4x^2\left(x-2\right)-9\left(x-2\right)\)
\(=\left(x-2\right)\left(2x-3\right)\left(2x+3\right)\)
9: \(x^3+2x^2-4x-8\)
\(=x^2\left(x+2\right)-4\left(x+2\right)\)
\(=\left(x+2\right)^2\cdot\left(x-2\right)\)
10: \(x^2-9-2xy+y^2\)
\(=\left(x-y\right)^2-9\)
\(=\left(x-y-3\right)\left(x-y+3\right)\)
11: \(x^2-4-4xy+4y^2\)
\(=\left(x-2y\right)^2-4\)
\(=\left(x-2y-2\right)\left(x-2y+2\right)\)
12: \(x^2-y^2+6y-9\)
\(=x^2-\left(y^2-6y+9\right)\)
\(=x^2-\left(y-3\right)^2\)
\(=\left(x-y+3\right)\left(x+y-3\right)\)
13: Ta có: \(25-x^2-2xy-y^2\)
\(=25-\left(x+y\right)^2\)
\(=\left(5-x-y\right)\left(5+x+y\right)\)
14: Ta có: \(3\left(2x-1\right)^2-12\)
\(=3\left(2x-1-2\right)\left(2x-1+2\right)\)
\(=3\left(2x-3\right)\left(2x+1\right)\)
15: Ta có: \(2\left(3x-1\right)^2-8\)
\(=2\left(3x-1-2\right)\left(3x-1+2\right)\)
\(=6\left(x-1\right)\left(3x+1\right)\)
16: Ta có: \(16-4x^2+12xy-9y^2\)
\(=16-\left(2x-3y\right)^2\)
\(=\left(4-2x+3y\right)\left(4+2x-3y\right)\)
17: Ta có: \(2x-2y-x^2+2xy-y^2\)
\(=2\left(x-y\right)-\left(x-y\right)^2\)
\(=\left(x-y\right)\left(2-x+y\right)\)
18: Ta có: \(2x^4+16x\)
\(=2x\left(x^3+8\right)\)
\(=2x\left(x+2\right)\left(x^2-2x+4\right)\)
19: Ta có: \(16x^2-2y^3\)
\(=2\left(8x^2-y^3\right)\)
20: Ta có: \(5x^3-5\)
\(=5\left(x^2-1\right)\)
\(=5\left(x-1\right)\left(x+1\right)\)
