Cách làm:
11) 5xy² - 10xyz + 5xz²
= 5xy² - 5xyz - 5xyz + 5xz²
= 5xy(y - z) - 5xz(y - z)
= (y-z)(5xy-5xz)
= 5x(y-z)²
12) x² - 4y² + x + 2y
= (x-2y)(x+2y) + (x+2y)
= (x+2y)(x-2y+1)
13) 9x - 16x³
= x(9-16x²)
= x(3-4x)(3+4x)
14) x² + y² -2xy +2x - 2y
= (x²-2xy+y²)+2(x-y)
= (x-y)² + 2(x-y)
= (x-y)(x-y+2)
15) 3x² - 5x +2
= 3x² - 3x - 2x + 2
= 3x(x-1) - 2(x-1)
= (x-1)(3x-2)
16) (x²+x+4)² + 8x(x²+x+4) + 15x²
= (x²+x+4)² + 8x(x²+x+4) + 24x² - 9x²
= (x²+x+4)² - 9x² + 8x(x²+x+4) + 24x²
= (x²+4x+4)(x²-2x+4) + 8x(x²+4x+4)
= (x+2)²(x²+6x+4)
17) 5x² - 10x
= 5x(x-2)
18) x² - y² + 2y - 2x
= (x-y)(x+y) - 2(x-y)
= (x-y)(x+y-2)
19) x² - 5x -14
= x² - 7x + 2x -14
= x(x-7) + 2(x-7)
= (x-7)(x+2)
20) 8x² - 10x +3
= 8x² - 4x - 6x + 3
= 4x(2x-1) - 3(2x-1)
= (2x-1)(4x-3)
Đó là cách làm của tôi
