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\(A=x^4-14x^3+71x^2-154x+120\)
\(=x^3\left(x-2\right)-12x^2\left(x-2\right)+47x\left(x-2\right)-60\left(x-2\right)\)
\(=\left(x-2\right)\left(x^3-12x^2+47x-60\right)\)
\(=\left(x-2\right)\left[x^2\left(x-3\right)-9x\left(x-3\right)+20\left(x-3\right)\right]\)
\(=\left(x-2\right)\left(x-3\right)\left(x^2-9x+20\right)=\left(x-2\right)\left(x-3\right)\left(x-4\right)\left(x-5\right)\)
b, Vì A là tích của 4 số nguyên liên tiếp nên A chia hết cho 24
\(x^4-14x^3+71x^2-154x+120\)
\(=x^4-2x^3-12x^3+24x^2+47x^2-94x-60x+120\)
\(=x^3\left(x-2\right)-12x^2\left(x-2\right)+47x\left(x-2\right)-60\left(x-2\right)\)
\(=\left(x-2\right)\left(x^3-12x^2+47x-60\right)\)
\(=\left(x-2\right)\left(x^3-3x^2-9x^2+27x+20x-60\right)\)
\(=\left(x-2\right)\left[x^2\left(x-3\right)-9x\left(x-3\right)+20\left(x-3\right)\right]\)
\(=\left(x-2\right)\left(x-3\right)\left(x^2-9x+20\right)\)
\(=\left(x-2\right)\left(x-3\right)\left(x^2-4x-5x+20\right)\)
\(=\left(x-2\right)\left(x-3\right)\left[x\left(x-4\right)-5\left(x-4\right)\right]\)
\(=\left(x-2\right)\left(x-3\right)\left(x-4\right)\left(x-5\right)\)
$x^4 - 14x^3 + 71x^2 - 154x + 120$
$= (x^4 - 14x^3 + 71x^2 - 154x + 121) - 1$
$= (x^2 - 7x + 11)^2 - 1$
$= (x^2 - 7x + 10)(x^2 - 7x + 12)$
$= (x^2 - 5x - 2x + 10)(x^2 - 3x - 4x + 12)$
$= (x - 5)(x - 2)(x - 3)(x - 4)$
$=(x-2)(x-3)(x-4)(x-5)$
\(x^4-6x^3+12x^2-14x+3\)
= \(x^4-4x^3+x^2-2x^3+8x^2-2x+3x^2-12x+3\)
= \(x^2\left(x^2-4x+1\right)-2x\left(x^2-4x+1\right)+3\left(x^2-4x+1\right)\)
= \(\left(x^2-4x+1\right)\left(x^2-2x+3\right)\)
x4+7x3+14x2+14x+4
=x4+7x3+4x2+10x2+14x+4
=(x4+4x2+4)+(7x3+14x)+10x2
=(x2+2)2+7x(x2+2)+10x2
=(x2+2)2+2x(x2+2)+5x(x2+2)+10x2
=(x2+2)(x2+2+2x)+5x(x2+2+2x)
=(x2+2+2x)(x2+2+5x)
\(x^3-9x^2+14x\)
= \(x^3-7x^2-2x^2+14x\)
= \(x^2.\left(x-7\right)-2x.\left(x-7\right)\)
= \(\left(x-7\right).\left(x^2-2x\right)\)
= \(\left(x-7\right).\left(x-2\right).x\)
\(x^3-9x^2+14x\)
\(=x\left(x^2-9x+14\right)\)
\(=x\left(x^2-7x-2x+14\right)\)
\(=x\left[x\left(x-7\right)-2\left(x-7\right)\right]\)
\(=x\left(x-2\right)\left(x-7\right)\)
\(x^4-14x^3+71x^2-154x+120\)
\(=x^4-2x^3-12x^3+24x^2+47x^2-94x-60x+120\)
\(=x^3\left(x-2\right)-12x^2\left(x-2\right)+47x\left(x-2\right)-60\left(x-2\right)\)
\(=\left(x-2\right)\left(x^3-12x^2+47x-60\right)\)
\(=\left(x-2\right)\left(x^3-3x^2-9x^2+27x+20x-60\right)\)
\(=\left(x-2\right)\left[x^2\left(x-3\right)-9x\left(x-3\right)+20\left(x-3\right)\right]\)
\(=\left(x-2\right)\left(x-3\right)\left(x^2-9x+20\right)\)
\(=\left(x-2\right)\left(x-3\right)\left(x^2-4x-5x+20\right)\)
\(=\left(x-2\right)\left(x-3\right)\left[x\left(x-4\right)-5\left(x-4\right)\right]\)
\(=\left(x-2\right)\left(x-3\right)\left(x-4\right)\left(x-5\right)\)