分解因式:(x^3+3x+2)(x^2+3x+4)-48

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分解因式:(x^3+3x+2)(x^2+3x+4)-48

分解因式:(x^3+3x+2)(x^2+3x+4)-48
分解因式:(x^3+3x+2)(x^2+3x+4)-48

分解因式:(x^3+3x+2)(x^2+3x+4)-48
=(x²+3x+2)(x²+3x+2+2)-48
=(x²+3x+2)²+2(x²+3x+2)-48
=(x²+3x+2+8)(x²+3x+2-6)
=(x²+3x+10)(x²+3x-4)
=(x²+3x+10)(x+4)(x-1)

设y=x²+3x+2,原式=y(y+2)-48=y²+2y-48=(y+8)(y-6)
代入整理为(x²+3x+2+8)(x²+3x+2-6)=(x²+3x+10)(x²+3x-4)=(x²+3x+10)(x+4)(x-1)

换元法:将x²+3x=y,
(y+2)(y+4)-48
=y²+6y+8-48
=y²+6y-40
=(y+10)(y-4)
=(x²+3x+10)(x²+3x-4)
=(x²+3x+10)(x+4)(x-1)