先化简,再求值:(2x+1)(x+2)-(x-2)²-(x+2)²,其中x=-1又1/2
先化简,再求值:(2x+1)(x+2)-(x-2)²-(x+2)²,其中x=-1又1/2
解:原式=(2x+1-x-2)(x+2)-(x-2)²
=(x-1)(x+2)-(x²-4x+4)
=x²+x-2-x²+4x-4
=5x-6
=5×(-1又1/2)-6
=-15/2-6
=-27/2
原式=(x+2)(2x+1-x-2)-(x-2)²
=(x+2)(x-1)-(x²-4x+4)
=x²+x-2-x²+4x-4
=5x-6
=5×(-1.5)-6
=-7.5-6
=-13.5
(2x+1)(x+2)-(x-2)²-(x+2)²
=(2x²+5x+2)-(x²-4x+4)-(x²+4x+4)
=2x²+5x+2-x²+4x-4-x²-4x-4
=5x-6 (将x=-1又1/2=-1.5代入)
=5×(-1.5)-6
=-7.5-6
=-13.5
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