5 :1/4  = 20 không phải 5/4 anh ơi 

\(\left(5x^5y^2z+\dfrac{1}{2}x^4y^2z^3-2xy^3z^2\right):\dfrac{1}{4}xy^2z\\ =\left(5:\dfrac{1}{4}\right).\left(x^5:x\right).\left(y^2:y^2\right).\left(z:z\right)+\left(\dfrac{1}{2}:\dfrac{1}{4}\right).\left(x^4:x\right).\left(y^2:y^2\right).\left(z^3:z\right)-\left(2:\dfrac{1}{4}\right).\left(x:x\right).\left(y^3:y^2\right).\left(z^2:z\right)\\ =20x^4+2x^3z^2-8yz\)

\((4x+y)^2-(4x-y)^2\\=[(4x+y)-(4x-y)][(4x+y)+(4x-y)]\\=(4x+y-4x+y)(4x+y+4x-y)\\=2y\cdot8x\\=16xy\)

2x - 6 - 4x = 0

-2x = -6

x = 3

Vậy x = 3

\(2(x-3)-4x=0\\\Leftrightarrow 2x-6-4x=0\\\Leftrightarrow -2x-6=0\\\Leftrightarrow -2x=6\\\Leftrightarrow x=6:(-2)\\\Leftrightarrow x=-3\)

A. ( x -5 ) ( 7x + 1 ) - 7x ( x + 3)

= 7x² + x - 35x - 5 - 7x² - 21x

= (7x²-7x²) + (x - 35x - 21x) -5

= -56x - 5

B = (x² - 2x.2 + 2²) - x² + 1²

B = (x² - x²) - 4x + (2 + 1)

B= -4x +3

A. (x - 5)(7x + 1) - 7x(x + 3)

= 7x² + x - 35x - 5 - 7x² - 21x

= (7x² - 7x²) + (x - 35x - 21x) - 5

= -55x - 5

B. (x - 2)² - (x - 1)(x + 1)

= x² - 4x + 4 - x² + 1

= (x² - x²) - 4x + (4 + 1)

= -4x + 5

a. \(x^2\) - 9y²

= (\(x\))² - (3y)²

= (\(x\) - 3y)(\(x\) + 3y)

x² - 9y² = x² - (3y)²= (x - 3y)(x + 3y)

Bài `1`

`a, (x+2)^2 =x^2 +4x+4`

`b, (x-5)^2=x^2 -10x+25`

`c,(2x-y)^2=(2x)^2- 2*2x*y+y^2=4x^2-4xy+y^2`

`d,(3x^2-2y)^2= (3x^2)^2 - 2*3x^2*2y +(2y)^2=9x^4-12x^2y +4y^2`

`e,,(2x-y)(4x^2+2xy+y^2)= (2x)^3-y^3=8x^3-y^3`

`f,(x+3)(x^2-3x+9)=x^3+3^3=x^3+27`

Lời giải:

Diện tích đáy: $24.3:3=24$ (cm²)

Chiều cao đáy tam giác: $24.2:4=12$ (cm) 

Đáp án C.

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(2x + 1)^2 - (x - 1)^2 = 0

=> 2x + 1 = x - 1 hoặc 2x + 1 = 1 - x

=> x = -2 hoặc x = 0