9)125+150x+60x2+8x3=... 12)x3+125y3
10)y3+12y2+48y+64=...
11)8x3-y3=...
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2: \(=\dfrac{\left(x-y\right)\left(x+y\right)\left(x^2+y^2\right)}{-\left(x-y\right)\left(x^2+xy+y^2\right)}=\dfrac{-\left(x+y\right)\left(x^2+y^2\right)}{x^2+xy+y^2}\)
a,x3+3x2+3x+1
b,x2+6x+9
c,-x3+9x2-27x+27
d,x2+4x+4
k,10x-25-x2
f,(x+y)2-9x2
g,8x3+42x2y+16xy2+6xy+y3
a) \(x^3+3x^2+3x+1=x^2+3\cdot x^2\cdot1+3\cdot x\cdot1^2+1^3=\left(x-1\right)^3\)
b) \(x^2+6x+9=x^2+2\cdot3\cdot x+3^2=\left(x+3\right)^2\)
c) \(-x^3+9x^2-27x+27\)
\(=-\left(x^3-9x^2+27x-27\right)\)
\(=-\left(x^3-3\cdot3\cdot x^2+3\cdot3^2\cdot x-3^3\right)=-\left(x-3\right)^3\)
d) \(x^2+4x+4=x^2+2\cdot2\cdot x+2^2=\left(x+2\right)^2\)
k) \(10x-25-x^2=-x^2+10x-25=-\left(x^2-10x+25\right)\)
\(=-\left(x^2-2\cdot5\cdot x+5^2\right)=-\left(x-5\right)^2\)
f) \(\left(x+y\right)^2-9x^2=\left(x-y\right)^2-\left(3x\right)^2=\left[\left(x-y\right)-3x\right]\left[\left(x-y\right)+3x\right]\)
\(=\left(x-y-3x\right)\left(x-y+3x\right)=\left(-2x-y\right)\left(4x-y\right)\)
Ta có
A = 8 x 3 – 12 x 2 y + 6 x y 2 – y 3 + 12 x 2 – 12 x y + 3 y 2 + 6 x – 3 y + 11 = ( 2 x ) 3 – 3 . ( 2 x ) 2 . y + 3 . 2 x . y - y 3 + 3 ( 4 x 2 – 4 x y + y 2 ) + 3 ( 2 x – y ) + 11 = ( 2 x – y ) 3 + 3 ( 2 x – y ) 2 + 3 ( 2 x – y ) + 1 + 10 = ( 2 x – y + 1 ) 3 + 10
Thay 2x – y = 9 vào A = ( 2 x – y + 1 ) 3 + 10 ta được
A = ( 9 + 1 ) 3 + 10 = 1010
Vậy A = 1010
Đáp án cần chọn là: C
\(a,=8\left(x^3-125\right)=8\left(x-5\right)\left(x^2+5x+25\right)\\ b,=\left(0,1+4x\right)\left(0,01-0,4x+16x^2\right)\\ c,=\left(x+\dfrac{1}{5}y\right)\left(x^2-\dfrac{1}{5}xy+\dfrac{1}{25}y^2\right)\\ d,=\left(3x-\dfrac{1}{2}y\right)\left(9x^2+\dfrac{3}{2}xy+\dfrac{1}{4}y^2\right)\\ e,=\left(x-1+3\right)\left[\left(x-1\right)^2-3\left(x-1\right)+9\right]\\ =\left(x+2\right)\left(x^2-2x+1-3x+3+9\right)\\ =\left(x+2\right)\left(x^2-5x+13\right)\\ f,=\left(\dfrac{x^2}{2}-y^2\right)\left(\dfrac{x^4}{4}+\dfrac{x^2y^2}{2}+y^4\right)\)
\(8x^3+4x^2-y^3-y^2\\ =\left(8x^3-y^3\right)+\left(4x^2-y^2\right)\)
\(=\left(2x-y\right)\left(4x^2+2xy+y^2\right)+\left(2x-y\right)\left(2x+y\right)\\ =\left(2x-y\right)\left(4x^2+2xy+y^2+2x+y\right)\)
\(9,=\left(5+2x\right)^3\\ 10,=\left(y+4\right)^3\\ 11,=\left(2x-y\right)\left(4x^2+2xy+y^2\right)\\ 12,=\left(x+5y\right)\left(x^2-5xy+25y^2\right)\)