phân tích thành nhân tử 9.(x+4/3)(x+2/3)(x-1/3)(x-1)-4x(x+1/3)
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1) x3 + 5x2 + 3x - 9
= x3 + 2x2 + 3x2 + 6x - 3x - 9
= ( x3 + 2x2 ) + (3x2 + 6x ) - ( 3x + 9 )
= x2 ( x+ 2 ) + 3x ( x + 2) - 3( x +2 )
= ( x + 2 ) ( x2 + 3x -3 )
2) x3 + 5x2 + 8x + 4
= ( x3 + x2 ) + ( 4x2 + 4x ) + ( 4x + 4 )
= x2 ( x + 1 ) + 4x ( x + 1 ) + 4 ( x + 1 )
= ( x + 1) ( x2 + 4x + 4 )
= (x + 1 ) ( x + 2 )2
3) x3 - 9x2 + 6x + 16
= x3 - 8x2 - x2 + 8x - 2x + 16
= ( x3 - 8x2 ) - ( x2 - 8x ) - ( 2x - 16 )
= x2 ( x - 8 ) - x ( x - 8 ) - 2 ( x - 8 )
= ( x - 8 ) ( x2 - x - 2 )
4) x3 - 4x2 + x + 6
= x3 - 3x2 - x2 + 3x - 2x + 6
= ( x3 - 3x2 ) - ( x2 - 3x ) - ( 2x - 6)
= x2 ( x - 3 ) - x ( x- 3 ) - 2 ( x - 3)
= ( x - 3 ) ( x2 - x - 2 )
\(4x^4+4x^2+1=\left(2x^2+1\right)^2\)
\(9x^4-6x^2+1=\left(3x^2-1\right)^2\)
\(\dfrac{x^2}{9}-\dfrac{2}{3}x+1=\left(\dfrac{x}{3}+1\right)^2\)
\(x^2-25=\left(x-5\right)\left(x+5\right)\)
\(a,x^4+4x^2-5\)
\(=x^4+4x^2+4-9\)
\(=\left(x^2+2\right)^2-3^2\)
\(=\left(x^2+5\right)\left(x^2-1\right)\)
Lời giải:
a.
$x^4+10x^3+26x^2+10x+1$
$=(x^4+10x^3+25x^2)+x^2+10x+1$
$=(x^2+5x)^2+2(x^2+5x)+1-x^2$
$=(x^2+5x+1)^2-x^2=(x^2+5x+1-x)(x^2+5x+1+x)$
$=(x^2+4x+1)(x^2+6x+1)$
b.
$x^4+x^3-4x^2+x+1$
$=(x^4-x^2)+(x^3-x^2)+(x-x^2)+(1-x^2)$
$=x^2(x-1)(x+1)+x^2(x-1)-x(x-1)-(x-1)(x+1)$
$=(x-1)[x^2(x+1)+x^2-x-(x+1)]$
$=(x-1)(x^3+2x^2-2x-1)$
$=(x-1)[(x^3-1)+(2x^2-2x)]=(x-1)[(x-1)(x^2+x+1)+2x(x-1)]$
$=(x-1)(x-1)(x^2+x+1+2x)=(x-1)^2(x^2+3x+1)$
Ta có: \(9\left(x+\frac43\right)\left(x+\frac23\right)\left(x-\frac13\right)\left(x-1\right)-4x\left(x+\frac13\right)\)
\(=9\left(x^2-x+\frac43x-\frac43\right)\left(x^2-\frac13x+\frac23x-\frac29\right)-4x\left(x+\frac13\right)\)
\(=9\left(x^2+\frac13x-\frac43\right)\left(x^2+\frac13x-\frac29\right)-4x\left(x+\frac13\right)\)
\(=9\left\lbrack\left(x^2+\frac13x\right)^2-\frac{14}{9}\cdot\left(x^2+\frac13x\right)+\frac{8}{27}\right\rbrack-4\left(x^2+\frac13x\right)\)
\(=9\cdot\left(x^2+\frac13x\right)^2-14\left(x^2+\frac13x\right)+\frac83-4\left(x^2+\frac13x\right)\)
\(=9\left(x^2+\frac13x\right)^2-18\left(x^2+\frac13x\right)+\frac83\)
\(=9\left(x^2+\frac13x\right)^2-18\left(x^2+\frac13x\right)+9-\frac{19}{3}\)
\(=\left\lbrack3\left(x^2+\frac13x\right)-3\right\rbrack^2-\frac{19}{3}=\left\lbrack3x^2+x-3\right\rbrack^2-\frac{57}{9}\)
\(=\left(3x^2+x-3-\frac{\sqrt{57}}{3}\right)\left(3x^2+x-3+\frac{\sqrt{57}}{3}\right)\)