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a,\(xy+3x-7y-21\)
\(=x\left(y+3\right)-7\left(y+3\right)\)
\(=\left(y+3\right)\left(x-7\right)\)
\(b,2xy-15-6x+5y\)
\(=\left(2xy-6x\right)+\left(-15+5y\right)\)
\(=2x\left(y-3\right)-5\left(3-y\right)\)
\(=2x\left(y-3\right)+5\left(y-3\right)\)
\(=\left(y-3\right)\left(2x+5\right)\)
a) \(4x^3y-12x^2y^3-8x^4y^3\)
\(=4x^2y\left(x-3y^2-2x^2y^2\right)\)
b) \(2x^2+4x+2-2y^2\)
\(=2\left(x^2+2x+1-y^2\right)\)
\(=2\left[\left(x+1\right)^2-y^2\right]\)
\(=2\left(x-y+1\right)\left(x+y+1\right)\)
c) \(x^3-2x^2+x-xy^2\)
\(=x\left(x^2-2x+1-y^2\right)\)
\(=x\left[\left(x-1\right)^2-y^2\right]\)
\(=x\left(x-y-1\right)\left(x+y-1\right)\)
d) \(x\left(x-2y\right)+3\left(2y-x\right)\)
\(=x\left(x-2y\right)-3\left(x-2y\right)\)
\(=\left(x-3\right)\left(x-2y\right)\)
e) \(x^2+4\)
\(=\left(x^4+4x^2+4\right)-4x^2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2-2x+2\right)\left(x^2+2x+2\right)\)
f) \(5x^2-7x-6\)
\(=\left(5x^2-10x\right)+\left(3x-6\right)\)
\(=5x\left(x-2\right)+3\left(x-2\right)\)
\(=\left(5x+3\right)\left(x-2\right)\)
a) \(x^4-2x^2+1=\left(x^2-1\right)^2=\left(x-1\right)^2\left(x+1\right)^2\)
b) \(x^2-y^2-5x+5y=\left(x-y\right)\left(x+y\right)-5\left(x-y\right)=\left(x-y\right)\left(x+y-5\right)\)
c) \(2x^3-x^2-8x+4\)
\(=x^2\left(2x-1\right)-4\left(2x-1\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(2x-1\right)\)
d) \(x\left(x-y\right)^2+y\left(x-y\right)^2-xy+x^2\)
\(=\left(x+y\right)\left(x-y\right)^2+x\left(x-y\right)\)
\(=\left(x-y\right)\left(x^2-y^2+x\right)\)
e) \(2x^2-5x+2\)
\(=\left(2x^2-x\right)-\left(4x-2\right)\)
\(=x\left(2x-1\right)-2\left(2x-1\right)\)
\(=\left(x-2\right)\left(2x-1\right)\)
a. \(\left(x+y\right)^3+\left(x-y\right)^3\)
\(=x^3+3x^2y+3xy^2+y^3+x^3-3x^2y+3xy^2-y^3\)
\(=2x^3+6xy^2\)
\(=2x\left(x^2+6y^2\right)\)
b. \(x^3-y^3+2x^2-2y^2\)
\(=\left(x-y\right)\left(x^2+xy+y^2\right)+2\left(x^2-y^2\right)\)
\(=\left(x-y\right)\left(x^2+xy+y^2\right)+2\left(x+y\right)\left(x-y\right)\)
\(=\left(x-y\right)\left(x^2+xy+y^2+2x+2y\right)\)
c. \(x^3-y^3-3x^2+3x-1\)
\(=\left(x^3-3x^2+3x-1\right)-y^3\)
\(=\left(x-1\right)^3-y^3\)
\(=\left(x-1-y\right)\left[\left(x-1\right)^2+\left(x-1\right)y+y^2\right]\)
\(=\left(x-y-1\right)\left(x^2+y^2+xy-2x-y+1\right)\)
Ta có:
a) 6x2y - 3y2 - 2x2 + y = (6x2y - 2x2) - (3y2 - y) = 2x2(3y - 1) - y(3y - 1) = (2x2 - y)(3y - 1)
b) 2x2 + x - 4xy - 2y + 2x + 1 = (x2 + x) - (4xy + 2y) + (x2 + 2x + 1) = x(x + 1) - 2y(2x + 1) + (x + 1)2
= (x + x + 1)(x + 1) - 2y(2x + 1) = (2x + 1)(x + 1) - 2y(2x + 1) = (2x + 1)(x + 1 - 2y)
c) 16x2y - 4xy2 - 4x3 + x2y = 4xy(4x - y) - x2(4x - y) = (4xy - x2)(4x - y)
d) 4x2 - 20x + 25 - 36y2 = (2x - 5)2 - (6y)2 = (2x - 5 - 6y)(2x - 5 + 6y)
e) x2 - 4y2 + 6x - 4y + 8 = (x2 + 6x + 9) - (4y2 + 4y + 1) = (x + 3)2 - (2y + 1)2 = (x + 3 - 2y - 1)(x + 3 + 2y + 1) = (x + 2 - 2y)(x + 4 + 2y)
g) Ta có : x10 + x5 + 1
= (x10 - x) + (x5 - x2) + (x2 + x + 1)
= x(x9 - 1) + x2(x3 - 1) + (x2 + x + 1)
= x(x3 - 1)(x6 + x3 + 1) + x2(x3 - 1) + (x2 + x + 1)
= (x7 + x4 + x)(x - 1)(x2 + x + 1) + x2(x - 1)(x2 + x + 1) + (x2 + x + 1)
= (x2 + x + 1)(x8 - x7 + x 5 - x4 + x2 - x + x4 + x3 + x2 + 1)
= (x2 + x + 1)(x8 - x7 + x5 + x3 - x + 1)
h) TT trên (dài dòng ktl)
`4x^3 y^2 - 8x^2 y^3 + 2x^4 y`
`= 2 x^2 y . (2x y - 4 y^2 + x^2`
`x^2 y + xy+ x + 1`
`= (x^2 y + xy)+ (x + 1)`
`= xy (x + 1) + (x+1) `
`= (xy + 1)(x+1) `
`6x +3 - (2x - 5) (2x + 1) `
`= 6x + 3 - (4x^2 - 10x + 2x - 5) `
`= 6x + 3 - (4x^2 - 8x - 5) `
`= 6x + 3 - 4x^2 + 8x + 5`
`= -4x^2 + 14x + 8 `
`= -(x - 4) (2x + 1) `
`x^2 - 2x - y^2 - 2y` (sửa đề)
`= (x^2 - y^2) - (2x + 2y) `
`= (x+y)(x-y) - 2 (x+y) `
`= (x+y)(x - y - 2)`
g; 16.(\(x\) - y)2 - (2\(x\) - 3)2
= [4.(\(x\) - y)]2 - (2\(x\) - 3)2
= [4(\(x\) - y) - (2\(x\) - 3)][4.(\(x\) - y) + (2\(x\) - 3)]
= [4\(x\) - 4y - 2\(x\) + 3][4\(x\) - 4y + 2\(x\) - 3]
= [(4\(x\) - 2\(x\)) - 4y + 3][(4\(x\) + 2\(x\)) - 4y + 3]
= [2\(x\) - 4y + 3][6\(x\) - 4y - 3]