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huj sáng cũng làm 1 bài cho bạn bấy giờ nghĩ lại làm chi cho tốn thời gian
a/ x^3-3x^2-4x+12
=x2(x-3)-4(x-3)
=(x-3)(x2-4)
=(x-3)(x-2)(x+2)
b/ x^4-5x^2+4
=x4-4x2+4-x2
=(x2-2)2-x2
=(x2-x-2)(x2+x-2)
=(x2-x-2)(x2-x+2x-2)
=(x2-x-2)[x(x-1)+2(x-1)]
=(x2-x-2)(x-1)(x+2)
TL:
\(3,3x^2-6xy+3y^2\)
\(=3\left(x^2-2xy+y^2\right)\)
\(=3\left(x-y\right)^2\)
\(x^4+2x^3+x^2=x^2.x^2+x^2.2x+x^2\)
\(=x^2.\left(x^2+2x+1\right)\)
\(=x^2\left(x+1\right)^2\)
a) \(x^2+4x+3\)
\(=x^2+3x+x+3\)
\(=x\left(x+3\right)+\left(x+3\right)\)
\(=\left(x+1\right)\left(x+3\right)\)
1) (3x+4)(x+1) = 3x2+7x+4 đặt là a
(6x+7)2= 36x2+84x+49 = 12a+1
=> a(12a+1)- 6 = 12a2 -a -6 = (3a+2)(4a-3) = (9x2+21x+14)(12x2+28x+13)
2) (x-2)2=x2-4x+4 đặt là a
(2x-5)(2x-3)= 4x2-16x+15 =4a-1
=> a(4a-1)-5 = 4a2-a-5 = (4a-5)(a+1) = ( 4x2-16x+11)(x2-4x+5)
3) đặt (x+3)2 =a ta làm tương tự
4) (x-2)(x-10)(x-4)(x-5) = (x2-12x+20)(x2-9x+20)
đặt x2+20=a => (a-12x)(a-9x)-54x2 = a2-21ax+54x2 = (a-18x)(a-3x) = (x2-18x+20)(x2-3x+20)
\(x^5-3x^4-x^3-x^2+3x+1\)
\(=\left(x^5-x^2\right)-\left(3x^4-3x\right)-\left(x^3-1\right)\)
\(=x^2\left(x^3-1\right)-3x\left(x^3-1\right)-\left(x^3-1\right)\)
\(=\left(x^3-1\right)\left(x^2-3x-1\right)\)
\(=\left(x-1\right)\left(x^2+x+1\right)\left(x^2-2.x.\frac{3}{2}+\frac{9}{4}-\frac{9}{4}-1\right)\)
\(=\left(x-1\right)\left(x^2+x+1\right)\left[\left(x-\frac{3}{2}\right)^2-\frac{13}{4}\right]\)
\(=\left(x-1\right)\left(x^2+x+1\right)\left(x-\frac{3}{2}-\frac{\sqrt{13}}{2}\right)\left(x-\frac{3}{2}+\frac{\sqrt{13}}{2}\right)\)
\(x^5-3x^4-x^3-x^2+3x+1\)\(1\)\(=\left(x^5-x^4\right)-\left(2x^4-2x^3\right)-\left(3x^3-3x^2\right)-\left(4x^2-4x\right)-\left(x-1\right)\)
\(=x^4\left(x-1\right)-2x^3\left(x-1\right)-3x^2\left(x-1\right)-4x\left(x-1\right)-\left(x-1\right)\)
\(=\left(x-1\right)\left(x^4-2x^3-3x^2-4x-1\right)\)
2x( x - 1 ) - x( 1 - x )2 - ( 1 - x )3
= 2x( x - 1 ) - x( x - 1 )2 + ( x - 1 )3
= ( x - 1 )[ 2x - x( x - 1 ) + ( x - 1 )2 ]
= ( x - 1 )( 2x - x2 + x + x2 - 2x + 1 )
= ( x - 1 )( x + 1 )
Ta có: \(2x\left(x-1\right)-x\left(1-x\right)^2-\left(1-x\right)^3\)
\(=\left(x-1\right)\left(2x-x^2+x+x^2-2x+1\right)\)
\(=\left(x-1\right)\left(x+1\right)\)
\(x^6-x^4+2x^3+2x^2\)
\(=x^2\left(x^4-x^2+2x+2\right)\)
\(=x^2\left[x^2\left(x^2-1\right)+2\left(x+1\right)\right]\)
\(=x^2\left[x^2\left(x-1\right)\left(x+1\right)+2\left(x+1\right)\right]\)
\(=x^2\left(x+1\right)\left(x^3-x^2+2\right)\)
\(=x^2\left(x+1\right)\left(x^3-2x^2+2x+x^2-2x+2\right)\)
\(=x^2\left(x+1\right)\left[x\left(x^2-2x+2\right)+\left(x^2-2x+2\right)\right]\)
\(=x^2\left(x+1\right)^2\left(x^2-2x+2\right)\)