比较(x+1)(x²-x+2)与(x-1)(x²+x+2)的大小
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(x+1)(x²-x+2)
=(x+1)(x²-x+1+1)
=(x+1)(x²-x+1)+(x+1)
=x³+1+x+1
=x³+x+2
(x-1)(x²+x+2)
=(x-1)(x²+x+1+1)
=(x-1)(x²+x+1)+(x-1)
=x³-1+x-1
=x³+x-2
因为：x³+x+2＞x³+x-2
所以，(x+1)(x²-x+2)＞(x-1)(x²+x+2)
=(x+1)(x²-x+1+1)
=(x+1)(x²-x+1)+(x+1)
=x³+1+x+1
=x³+x+2
(x-1)(x²+x+2)
=(x-1)(x²+x+1+1)
=(x-1)(x²+x+1)+(x-1)
=x³-1+x-1
=x³+x-2
因为：x³+x+2＞x³+x-2
所以，(x+1)(x²-x+2)＞(x-1)(x²+x+2)
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