9 Phân tích đa thức sau thành nhân tử:
a) 9xy^2-18x^2y ; b) 6x^2-2y ; c)7x(x-y)-14y(y-x)
d)7-x^2 ; e) 16+8x+x^2 ; f)1-27x^3
g) x^3-9x^2+27x-27 ; h) (x+2y)^2-16y^2 ; i) x^3-64y^3
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a) \(x^3y^3+x^2y^2+4\)
\(=x^3y^3-x^2y^2+2x^2y^2-2xy+2xy+4\)
\(=\left(x^3y^3-x^2y^2+2xy\right)+\left(2x^2y^2-2xy+4\right)\)
\(=xy\left(x^2y^2-xy+2\right)+2\left(x^2y^2-xy+2\right)\)
\(=\left(xy+2\right)\left(x^2y^2-xy+2\right)\)
b) \(x^3+3x^2y-9xy^2+5y^3\)
\(=x^3+5x^2y-2x^2y-10xy^2+xy^2+5y^3\)
\(=\left(5y^3-10xy^2+5x^2y\right)+\left(xy^2-2x^2y+x^3\right)\)
\(=5y\left(y^2-2xy+x^2\right)+x\left(y^2-2xy+x^2\right)\)
\(=\left(5y+x\right)\left(y^2-2xy+x^2\right)\)
\(=\left(5y+x\right)\left(y-x\right)^2\)
x3 + 3x2y - 9xy2 + 5y3
= ( x3 - 3x2y + 3xy2 - y3 ) + ( 6y3 - 12xy2 + 6 x2y )
= ( x - y )3 + 6y ( x - y )2
= ( x - y )2 ( x + 5y )
1: \(6x^2y-9xy^2+3xy\)
\(=3xy\left(2x-3y+1\right)\)
2: \(\left(4-x\right)^2-16\)
\(=\left(4-x-4\right)\left(4-x+4\right)\)
\(=-x\cdot\left(8-x\right)\)
3: \(x^3+9x^2-4x-36\)
\(=x^2\left(x+9\right)-4\left(x+9\right)\)
\(=\left(x+9\right)\left(x-2\right)\left(x+2\right)\)
1) \(6x^2y-9xy^2+3xy=3xy\left(2x-3y+1\right)\)
2) \(\left(4-x\right)^2-16=\left(4-x\right)^2-4^2=\left(4-x-4\right)\left(4-x+4\right)=-x\left(8-x\right)\)
3) \(x^3+9x^2-4x-36\\ =\left(x^3-2x^2\right)+\left(11x^2-22x\right)+\left(18x-36\right)\\ =x^2\left(x-2\right)+11x\left(x-2\right)+18\left(x-2\right)\\ =\left(x^2+11x+18\right)\left(x-2\right)\\ =\left[\left(x^2+2x\right)+\left(9x+18\right)\right]\left(x-2\right)\\ =\left[x\left(x+2\right)+9\left(x+2\right)\right]\left(x-2\right)\\ =\left(x+2\right)\left(x+9\right)\left(x-2\right)\)
phân tích đa thức thành nhân tử
a, 6x^2 + 7xy + 2y^2
=6x^2+3xy+4xy+2y^2
=3x(x+y)+2y(x+y)
=(3x+2y)(x+y)
b, 9x^2 - 9xy - 4y^2
=9x^2 +3xy-12xy-4y^2
=3x(x+y)-4y(x+y)
=(3x+4y)(x+y)
c, x^2 - y^2 + 10x - 6y + 16=x^2-y^2+6x-6y+4x+16=x(x+6)-y(x+6)+4(x+6)=(x-y+4)(x+6)
Bài làm
a, 6x2 + 7xy + 2y2
= 6x2 + 3xy + 4xy + 2y2
= ( 6x2 + 3xy ) + ( 4xy + 2y2 )
= 3x( 2x + y ) + 2y( 2x + y )
= ( 2x + y )( 3x + 2y )
b, 9x2 - 9xy - 4y2
= 9x2 - 12xy + 3xy - 4y2
= ( 9x2 - 12xy ) + ( 3xy - 4y2 )
= 3x( 3x - 4y ) + y ( 3x - 4y )
= ( 3x + y )( 3x - 4y )
c, x2 - y2 + 10x - 6y + 16
= x2 - y2 - 6x + 6y + 4x + 16
= x( x + 6 ) - y( x + 6 ) + 4( x + 6 )
= ( x - y + 4 )( x + 6 )
# Học tốt #
\(\Rightarrow\left(x^2+2x\right)^2+9\left(x^2+2x\right)+20=\left(x^2+2x\right)^2+4\left(x^2+2x\right)+5\cdot\left(x^2+2x\right)+20=\left(x^2+2x\right)\left(x^2+2x+4\right)+5\left(x^2+2x+4\right)=\left(x^2+2x+4\right)\left(x^2+2x+5\right)\)
câu b sai r
\(\dfrac{1}{3}xy+x^2z+xz=3x\left(\dfrac{1}{9}y+\dfrac{1}{3}xz+\dfrac{1}{3}z\right)\)
Lời giải:
a.
$=\frac{1}{2}(x^2-4y^2)=\frac{1}{2}[x^2-(2y)^2]=\frac{1}{2}(x-2y)(x+2y)$
b.
$=\frac{1}{3}x(y+3xz+3z)$
c.
$=\frac{2}{25}x(225x^2-4)=\frac{2}{25}(15x-2)(15x+2)$
d.
$=\frac{1}{5}x^2(2+25x+5y)$
\(\left(x^2+2x\right)^2+4\left(x^2+2x\right)+5\left(x^2+2x\right)+20\)
\(=\left(x^2+2x\right)\left(x^2+2x+4\right)+5\left(x^2+2x+4\right)\)
\(=\left(x^2+2x+5\right)\left(x^2+2x+4\right)\)