先化简,再求值x(x2-4)-(x+3)(x2-3x+2)-2x(x-2),其中x=1.5.
问题描述:
先化简,再求值x(x2-4)-(x+3)(x2-3x+2)-2x(x-2),其中x=1.5.
答
x(x2-4)-(x+3)(x2-3x+2)-2x(x-2)
=x3-4x-(x3-3x2+2x+3x2-9x+6)-2x2+4x
=x3-4x-x3+3x2-2x-3x2+9x-6-2x2+4x
=-2x2+7x-6
当x=1.5时,原式=-2×1.52+7×1.5-6=6-6=0