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`C(x)=`\(5-8x^4+2x^3+x+5x^4+x^2-4x^3\)
`C(x)= (-8x^4+5x^4)+(2x^3-4x^3)+x^2+x+5`
`C(x)= -3x^4-2x^3+x^2+x+5`
`D(x)=`\(\left(3x^5+x^4-4x\right)-\left(4x^3-7+2x^4+3x^5\right)\)
`D(x)= 3x^5+x^4-4x-4x^3+7-2x^4-3x^5`
`D(x)=(3x^5-3x^5)+(x^4-2x^4)-4x^3-4x+7`
`D(x)=-x^4-4x^3-4x+7`
`P(x)=C(x)+D(x)`
`P(x)=( -3x^4-2x^3+x^2+x+5)+(-x^4-4x^3-4x+7)`
`P(x)=-3x^4-2x^3+x^2+x+5-x^4-4x^3-4x+7`
`P(x)=(-3x^4-x^4)+(-2x^3-4x^3)+x^2+(x-4x)+(5+7)`
`P(x)=-4x^4-6x^3+x^2-3x+12`
`Q(x)=C(x)-D(x)`
`Q(x)=( -3x^4-2x^3+x^2+x+5)-(-x^4-4x^3-4x+7)`
`Q(x)=-3x^4-2x^3+x^2+x+5+x^4+4x^3+4x-7`
`Q(x)=(-3x^4+x^4)+(-2x^3+4x^3)+x^2+(x+4x)+(5-7)`
`Q(x)=-2x^4+2x^3+x^2+5x-2`
`F(x)=Q(x)-(-2x^4+2x^3+x^2-12)`
`F(x)=(-2x^4+2x^3+x^2+5x-2)-(-2x^4+2x^3+x^2-12)`
`F(x)=-2x^4+2x^3+x^2+5x-2+2x^4-2x^3-x^2+12`
`F(x)=(-2x^4+2x^4)+(2x^3-2x^3)+(x^2-x^2)+5x+(-2+12)`
`F(x)=5x+10`
Đặt `5x+10=0`
`\Leftrightarrow 5x=0-10`
`\Leftrightarrow 5x=-10`
`\Leftrightarrow x=-10 \div 5`
`\Leftrightarrow x=-2`
Vậy, nghiệm của đa thức là `x=-2.`
\(4x^4-21x^2y^2+y^4\)
\(=\left(4x^4+4x^2y^2+y^4\right)-25x^2y^2\)
\(=\left(2x^2+y^2\right)^2-\left(5xy\right)^2\)
\(=\left(2x^2+y^2-5xy\right)\left(2x^2+y^2+5xy\right)\)
\(a,4x^4-21x^2y^2+y^4=\left(2x^2\right)^2+4x^2y^2+y^4-4x^2y^2-21x^2y^2\)
\(=\left(2x^2+y^2\right)^2-25x^2y^2\)
\(=\left(2x^2+y^2-5xy\right)\left(2x^2+y^2+5xy\right)\)
\(b,x^5-5x^3+4x=x\left(x^4-5x^2+4\right)\)
\(=x\left(x^4-4x^2-x^2+4\right)\)
\(=x\left[x^2\left(x^2-4\right)-\left(x^2-4\right)\right]\)
\(=x\left(x^2-4\right)\left(x^2-1\right)\)
\(=x\left(x-2\right)\left(x+2\right)\left(x-1\right)\left(x+1\right)\)
\(c,x^3+5x^2+3x-9=x^3-x^2+6x^2-6x+9x-9\)
\(=x^2\left(x-1\right)+6x\left(x-1\right)+9\left(x-1\right)\)
\(=\left(x-1\right)\left(x^2+6x+9\right)\)
\(=\left(x-1\right)\left(x^2+3x+3x+9\right)\)
\(=\left(x-1\right)\left[x\left(x+3\right)+3\left(x+3\right)\right]\)
\(=\left(x-1\right)\left(x+3\right)\left(x+3\right)\)
\(=\left(x-1\right)\left(x+3\right)^2\)
\(d,x^{16}+x^8-2=x^{16}+2x^8-x^8-2\)
\(=x^8\left(x^8-1\right)+2\left(x^8-1\right)\)
\(=\left(x^8-1\right)\left(x^8+2\right)\)
a) 4x3y - 12x2y3 - 8x4y3 = 4x2y( x - 3y2 - 2x2y2 )
b) 2x2 + 4x + 2 - 2y2 = 2( x2 + 2x + 1 - y2 ) = 2[ ( x2 + 2x + 1 ) - y2 ] = 2[ ( x + 1 )2 - y2 ] = 2( x - y + 1 )( x + y + 1 )
c) x3 - 2x2 + x - xy2 = x( x2 - 2x + 1 - y2 ) = x[ ( x2 - 2x + 1 ) - y2 ] = x[ ( x - 1 )2 - y2 ] = x( x - y - 1 )( x + y - 1 )
d) x( x - 2y ) + 3( 2y - x ) = x( x - 2y ) - 3( x - 2y ) = ( x - 2y )( x - 3 )
e) x4 + 4 = ( x4 + 4x2 + 4 ) - 4x2 = ( x2 + 2 )2 - ( 2x )2 = ( x2 - 2x + 2 )( x2 + 2x + 2 )
f) 5x2 - 7x - 6 = 5x2 - 10x + 3x - 6 = 5x( x - 2 ) + 3( x - 2 ) = ( x - 2 )( 5x + 3 )
\(x^4+4=x^4+4x^2+4-4x^2=\left(x^2+2\right)^2-4x^2=\left(x^2+2x+2\right)\left(x^2-2x+2\right)\)
\(4x^8+1=\left(2x^4\right)^2+1=\left(2x^4\right)^2-2.2x^4+1+2.2.x^4=\left(2x^4+1\right)^2-4x^4\)
\(=\left(2x^4+2x^2+1\right)\left(4x^4-2x^2+1\right)\)
\(x^2-8x-9==x^2+x-9x-9=x\left(x+1\right)-9\left(x+1\right)=\left(x+1\right)\left(x-9\right)\)
\(x^2+14x+48=x^2+6x+8x+48=x\left(x+6\right)+8\left(x+6\right)=\left(x+6\right)\left(x+8\right)\)
a) \(x^4+4=x^4+4x^2+4-4x^2=\left(x^2+2\right)^2-4x^2=\left(x^2+2x+2\right)\left(x^2-2x+2\right)\)
b) \(4x^8+1=\left(2x^4\right)^2+1=\left(2x^4\right)^2-2.2x^4+1+2.2.x^4=\left(2x^4+1\right)^2-4x^4\)
c) \(x^2-8x-9==x^2+x-9x-9=x\left(x+1\right)-9\left(x+1\right)=\left(x+1\right)\left(x-9\right)\)
d) \(x^2+14x+48=x^2+6x+8x+48=x\left(x+6\right)+8\left(x+6\right)=\left(x+6\right)\left(x+8\right)\)