5x – 20y = 5x – 5.4y = 5(x – 4y)

a) \(5x-20y\)

\(=5\left(x-4y\right)\)

b) \(5x\left(x-1\right)-3x\left(x-1\right)\)

\(=2x\left(x-1\right)\) 

c) \(x\left(x+y\right)-5x-5y\)

\(=x\left(x+y\right)-5\left(x+y\right)\)

\(=\left(x-5\right)\left(x+y\right)\)

a)5x-20y

=5x-4*5y

=5(x-4y)

b)x(x-1)-3x(x-1)

=(x-3x)(x-1)

c)x(x+y)-5x-5y

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

=(x-5)(x+y)

5.(x-4)

tính nhanh .

a)  85 .12,7 + 5.3.12,7 = 12,7 . ( 85 + 5.3 ) = 12,7 . (85+15) = 12,7 . 100 = 1270

b)  52.143 - 52.39 - 8.26 = 52.143 - 52.39 - 4.2.26 = 52.143 - 52.39 - 4.52 = 52.( 143 -39 - 4 ) = 52 . 100 = 5200

phân tích :

5x - 20y = 5 .(x - 4y)

5x(x-1)-3x.(x-1) = (x-1).(5x-3x) = 2x(x-1)  hoặc 5x(x-1)-3x(x-1) = x(x-1)(5-3) = 2x(x-1)

x.(x+y)-5x-5y = x(x+y) - 5 (x+y) = (x+y)(x-5)

85.12,7+5.3 .12,7                                 

= (85+5.3.)12,7

= 100 . 12,7

=1270

52.143-52.39-8.26

=52 . 143 - 52 . 39 - 4 . 2 . 26 
= 52 . 143 - 52 . 39 - 52 . 4 
= 52 . ( 143 - 39 - 4) 
= 52 . 100 
= 5200

Ta có: 

a) 5x - 20y = 5(x - 4y)

b) 5x(x - 1) - 3x(x - 1) = x(x - 1)2

c) x(x + y) - 5x - 5y = x(x + y) - (5x + 5y) = x(x + y) - 5(x + y) = (x - 5)(x + y)

d) x² - 9 = (x - 3)(x + 3)

e) 4² - 25 = (4 - 5)(4 + 5) f) x⁶ - y⁶ = (x⁴)² - (y⁴)² = (x⁴ - y⁴)(x⁴ + y⁴) 

a)  5x - 20y = 5( x - 4y)

b) 5x(x-1) - 3x(x-1) =2x (x-1) 

c) x² - 9 = x² - 3² = ( x-3)(x+3)

e) 4²-25 = 4² - 5² = ( 4-5)(4+5)= -9

f) x⁶ - y⁶ = (x³)² - (y³)² = ( x³ - y³ ) ( x³ + y³)

                                    = (x-y) ( x² + xy + y² ) ( x+y) ( x² -xy +y²)

mình làm thiếu câu c ) x(x+y) - 5x-5y 

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

                                    = (x+y) ( x-5)

a) \(5x-20y\\ =5\left(x-4y\right)\)

b) \(5x\left(x-1\right)-3x\left(x-1\right)\\ =\left(5x-3x\right)\left(x-1\right)\\ =2x\left(x-1\right)\)

c) \(x\left(x+y\right)-5x-5y\\ =x\left(x+y\right)-\left(5x+5y\right)\\ =x\left(x+y\right)-5\left(x+y\right)\\ =\left(x+y\right)\left(x-5\right)\)

a) 5x-20y=5(x-4y)

b) 5x(x-1)-3x(x-1)

= (x-1)(5x-3x)

c) x(x+y)-5x-5y

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

=(x+y)(x-5)

a) 5x - 20y = 5(x - 4y)

b) 5x (x - 1) - 3x (x - 1) = (x - 1)(5x - 3x)

c)x (x + y) - 5x - 5y = x (x + y)-5 (x + y) = (x + y) (x - 5)

\(x^2+xy-20y^2\)

\(=x^2+2.x.\frac{1}{2}y+\frac{1}{4}y^2-20y^2-\frac{1}{4}y^2\) 

\(=\left(x+\frac{1}{2}y\right)^2-\frac{79}{4}\)

\(=\left(x+\frac{1}{2}y-\frac{\sqrt{79}}{2}\right)\left(x+\frac{1}{2}y+\frac{\sqrt{79}}{2}\right)\)

\(5y^3-10xy^2+5yx^2-20y=5y\left(y^2-2xy+x^2-4\right)\)

                                                              \(=5y\left[\left(x+y\right)^2-4\right]\)

                                                               \(=5y\left(x+y-2\right)\left(x+y+2\right)\)

Chúc bạn học tốt.