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Lời giải:
a.
$2x^4-7x^3-2x^2+13x+6$
$=(2x^4-4x^3)-(3x^3-6x^2)-(8x^2-16x)-(3x-6)$
$=2x^3(x-2)-3x^2(x-2)-8x(x-2)-3(x-2)$
$=(x-2)(2x^3-3x^2-8x-3)$
$=(x-2)[2x^2(x-3)+3x(x-3)+(x-3)]$
$=(x-2)(x-3)(2x^2+3x+1)$
$=(x-2)(x-3)[2x(x+1)+(x+1)]$
$=(x-2)(x-3)(x+1)(2x+1)$
b.
$(x^2+1)-x(a^2+1)$
Đa thức này không phân tích được thành nhân tử bạn nhé.
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= (x3-1)+3x(x-1) = (x-1)(x2+x+1)+3x(x-1)
=(x-1)(x2+x+1+3x)
=(x-1)(x2+4x+1)
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Đặt \(x^2-3x-1=a\), ta có:
\(a^2-12a+27=a^2-9a-3a+27=a\left(a-9\right)-3\left(a-9\right)=\left(a-9\right)\left(a-3\right)\)
\(=\left(x^2-3x-1-9\right)\left(x^2-3x-1-3\right)=\left(x^2-3x-10\right)\left(x^2-3x-4\right)\)
Mà \(x^2-3x-10=x^2-5x+2x-10=x\left(x-5\right)+2\left(x-5\right)=\left(x-5\right)\left(x+1\right)\)
và \(x^2-3x-4=x^2+x-4x-4=x\left(x+1\right)-4\left(x+1\right)=\left(x+1\right)\left(x-4\right)\)
\(\Rightarrow\left(x^2-3x-1\right)^2-12\left(x^2-3x-1\right)+27=\left(x-5\right)\left(x-4\right)\left(x+1\right)\left(x+2\right)\)
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ta có: x3 +1-3x2-3x
=(x+1)(x2 -x+1)-3x(x+1)
=(x+1)(x2 -x+1-3x)
=(x+1)(x2-4x+1)
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\(x^2-3x^2+1-3x\)
\(=\left(x^2+1\right)-3\left(x^2+1\right)\)
\(=\left(x^2+1\right)\left(1-3\right)\)
\(=-2\left(x^2+1\right)\)
- 3 nha ko phải -3x đâu
x2 - 3x2 + 1 - 3x
= (x2 + 1) + (-3x2 - 3x)
= x(x + 1) - 3x(x + 1)
= (x + 1) (x - 3x)
k bít đúng k?? 546456676577688789687684684623654654767576768745253563464545645
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có -1 thì không phân tích được, còn nếu là +1 thì phân tích được, bạn xem lại đề
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\(A=\left(x^2+3x+1\right)\left(x^2+3x-3\right)-5\)
Đặt \(t=x^2+3x+1\) thì A thành
\(t\left(t-4\right)-5=t^2-4t-5\)
\(t^2-5t+t-5=t\left(t-5\right)+\left(t-5\right)\)
\(=\left(t-5\right)\left(t+1\right)=\left(x^2+3x+1-5\right)\left(x^2+3x+1+1\right)\)
\(=\left(x^2+3x-4\right)\left(x^2+3x+2\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(x+2\right)\left(x+4\right)\)
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x3 - 3x2 - 3x - 1 -y3
= (x3 - y3) - (3x2 + 3x) - 1
= [(x-y)x2 + (x-y)xy + (x-y)y2 ] - 3x(x+1) -1
= (x-y)(x2+xy+y2) - 3x(x+1) - 1