bằng 1

( 8x – 1 ) ( 3x + 2) + ( 6x + 1 )( 3 – 4x) = 28

<=> 24x + 16x - 3x -2 + 18x - 24x + 3 - 4x =28

<=> 24x -24x +16x - 3x + 18x - 4x = 2 - 3 + 28 

<=> 27x = 27

<=> x=27/27

<=> x=1 

Vậy x=1

mình hơi ẩu làm lại :(

( 8x – 1 ) ( 3x + 2) + ( 6x + 1 )( 3 – 4x) = 28

=> 24x^2 + 16x - 3x - 2 + 18x - 24x^2 + 3 - 4x =28

=> 24x^2 - 24x^2 + 16x -3x+18x-4x = 2-3+28

=> 27x = 27

=> x=27/27

=> x=1

Vậy x=1

x3+2x2y+xy2−9xx3+2x2y+xy2−9x

=x(x2+2xy+y2−9)=x(x2+2xy+y2−9)

=x[(x+y)2−32]=x(x+y+3)(x+y−3)=x[(x+y)2−32]=x(x+y+3)(x+y−3)

b) 2x−2y−x2+2xy−y22x−2y−x2+2xy−y2

=2(x−y)−(x−y)2=(x−y)(2−x+y)=2(x−y)−(x−y)2=(x−y)(2−x+y)

c) x2−2x−4y2−4yx2−2x−4y2−4y

=(x2−4y2)−(2x+4y)=(x2−4y2)−(2x+4y)

=(x−2y)(x+2y)−2(x+2y)=(x−2y)(x+2y)−2(x+2y)

=(x+2y)(x−2y−2)

mik gửi lời mời kết bạn cho cậu rồi đó

M=5x^2+y^2+2x(y-2)+2021

<=> M = 5x^2 + y^2 + 2xy - 4x + 2021

<=> M = 4x^2 + x^2 + y^2 + 2xy - 4x + 1 + 2020

<=> M = ( 4x^2 - 4x + 1) + (x^2 +2xy+y^2) +2020

<=> M =(2x-1)^2 + (x+y)^2 + 2020

Vì: (2x-1)^2 + (x+y)^2  > 0

=> (2x-1)^2 + (x+y)^2 + 2020 > 2020

Dấu "=" xảy ra khi và chỉ khi : (2x-1)^2=0 => 2x-1 = 0 => 2x= 1 => x=1/2

                                                (x+y)^2=0 => x+y=0 => 1/2 + y =0 => y= 0- 1/2 => y=-1/2

Vậy Mmin = 2020 khi x=1/2;y=-1/2