x² - 4x -5

= x² - 5x + x -5

= x(x-5) + (x-5)

=(x+1)(x-5)

x^2-4x-4=x²-2.2.x-2²

           =[x-2]²

Lần sau bạn phải ghi cả đề ra chứ -.-

x³ - 3x² + 1 - 3x

= x³ + x² - 4x² -4x + x +1

=x²(x+1) -4x(x+1) + (x+1)

=(x+1)(x² - 4x+1) 

\(x^3\)\(-3x^2\)\(+1-3x\)

\(\left(x^3+1\right)\)\(-\left(3x^2-3x\right)\)

\(\left(x+1\right)\)\(\left(x^2-x+1\right)\)\(-3x\left(x+1\right)\)

\(\left(x+1\right)\)\(\left(x^2-x+1-3x\right)\)

\(\left(x+1\right)\)\(\left(x^2-4x+1\right)\)

2x² + 7x + 5

= 2x² + 2x + 5x + 5

= 2x(x+1) + 5(x+1)

=(2x+5)(x+1) 

16 - 5x² -3

= (16-3) - 5x²

= 13 - 5x²

mình mới lớp 5 hịc 

(x+5)(x+7) - (x-4)(3+x)

= (x² + 7x + 5x + 35) -(3x + x² - 12-4x)

=(x² +12x + 35) - (x² -x -12)

=x² +12x+35 - x² + x +12

= (x²-x²)+ (12x+ x) + (35+12)

= 13x + 47

\(=x^2+7x+5x+35-3x-x^2+12+4x\)

\(=13x+47\)

????????? where câu hỏi 

??? đăng j zdậy

4x(x² -x+1) -(4x-1)(x²-x)

= 4x³ - 4x² + 4x - (4x³ - 4x² - x² + x)

= 4x³ - 4x² + 4x - 4x³ + 4x² + x²-x

=(4x³ - 4x³) - (4x² - 4x²-x²)+ (4x-x) 

= x² + 3x 

4x(x^2-x+1)-(4x-1)(x^2-x)

=4x^3-4x^2+4x-4x^3+4x^2+x^2-x

=x^2+3x

3x³ + 6x²y+ 3xy²

=3x³ + 3x²y + 3x²y + 3xy²

= 3x²(x +y) + 3xy(x +y)

=(x+y)(3x² + 3xy)

= 3x(x+y)(x+y)

= 3x(x+y)²