thôi mik làm đc r

A = x³ + 3x² + 3x - 899

= (x³ + 3x² + 3x + 1) - 900

= (x + 1)³ - 900

= (29 + 1)³ - 900 = 30³ - 900 = 26100

B = x³ - 6x² + 12x + 10

= (x³ - 6x² + 12x - 8) + 18

= (x - 2)³ + 18

= (12 - 2)³ + 18 = 10³ + 18 = 1000 + 18 = 1018

c) C = 8x³ - 27y³

= (2x)³ - (3y)³

= (2x - 3y)(4x² + 6xy + 9y²)

= (2x - 3y)(4x² - 12xy + 9y²) + (2x - 3y).18xy

= (2x - 3y)(2x - 3y)² + (2x - 3y).18xy

= (2x - 3y)³ + (2x - 3y).18xy

= 5³ + 5.18.4

= 125 - 360

= -235

D = x³ + y³ + 3xy(x² + y²) + 6x²y²(x + y)

= (x + y)(x² - xy + y²) + 3x³y + 3xy³ + 6x²y²

= x² + y² - xy + 3x³y + 3xy³ + 6x²y² 

= (x + y)² - 3xy + 3x³y + 3xy³ + 6x²y² 

= 1 - 3xy(2xy - 1) + 3xy(x² + y²)

= 1 - 3xy(x² + y² + 2xy - 1)

= 1 - 3xy[(x + y)² - 1]

= 1 - 0 = 1

bn làm đc câu này chưa vậy

a: \(\dfrac{7x^3y^4}{35xy}=\dfrac{7xy\cdot x^2y^3}{35xy}=\dfrac{x^2y^3}{5}\)

b: \(\dfrac{x^3-4x}{10-5x}=\dfrac{-x\left(x-2\right)\left(x+2\right)}{5\left(x-2\right)}=\dfrac{-x^2-2x}{5}\)

c: \(\dfrac{\left(x+2\right)\left(x+1\right)}{x^2-1}=\dfrac{\left(x+2\right)\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}=\dfrac{x+2}{x-1}\)

d: \(\dfrac{x^2-x-2}{x+1}=\dfrac{\left(x-2\right)\left(x+1\right)}{x+1}=x-2=\dfrac{\left(x-2\right)\left(x-1\right)}{x-1}=\dfrac{x^2-3x+2}{x-1}\)

e: \(\dfrac{x^3+8}{x^2-2x+4}=\dfrac{\left(x+2\right)\left(x^2-2x+4\right)}{x^2-2x+4}=x+2\)

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

b) \(x^2+16x+64=\left(x+8\right)^2\)

c) \(x^3-8y^3=x^3-\left(2y\right)^3\)

\(=\left(x-2y\right)\left(x^2+2xy+4y^2\right)\)

d) \(9x^2-12xy+4y^2=\left(3x-2y\right)^2\)

d.Câu hỏi của Nguyễn Mai - Toán lớp 9 - Học toán với OnlineMath