1.(x^2-x-2)(x^2+11x+28)-19 2.(x-2)(x+1)(x-4)(x+8)+54x^2 注:不用换元法,因式分解

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1.(x^2-x-2)(x^2+11x+28)-19 2.(x-2)(x+1)(x-4)(x+8)+54x^2 注:不用换元法,因式分解
1.(x^2-x-2)(x^2+11x+28)-19 2.(x-2)(x+1)(x-4)(x+8)+54x^2 注:不用换元法,因式分解

1.(x^2-x-2)(x^2+11x+28)-19 2.(x-2)(x+1)(x-4)(x+8)+54x^2 注:不用换元法,因式分解
1.(x^2-x-2)(x^2+11x+28)-19
=(x+1)(x-2)(x+4)(x+7)-19
=[(x+1)(x+4)][(x-2)(x+7)]-19
=[x^2+5x+4][x^2+5x-14]
=(x^2+5x)^2-10(x^2+5x)-56-19
=(x^2+5x)^2-10(x^2+5x)-75
=(x^2+5x+5)(x^2+5x-15)
=[x+(5+√5)/2][x+(5-√5)/2][x+(5+√85)/2][x+(5-√85)/2] (这一步如果算错了,请多包涵)
2.(x-2)(x+1)(x-4)(x+8)+54x^2
=[(x-2)(x-4)][(x+1)(x+8)]+54x^2
=[x^2+8-6x][x^2+8+9x]+54x^2
=(x^2+8)+3x(x^2+8)-54x^2+54x^2
=(x^2+8)+3x(x^2+8)
=(x^2+8)(x^2+3x+8)
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