先化简,再求值:5x(x2-2x+4)-x2(5x-2)+(-4x)(2-2x),其中x=-5/12.
问题描述:
先化简,再求值:5x(x2-2x+4)-x2(5x-2)+(-4x)(2-2x),其中x=-
. 5 12
答
5x(x2-2x+4)-x2(5x-2)+(-4x)(2-2x)
=5x3-10x2+20x-5x3+2x2-8x+8x2
=12x,
当x=-
时,5 12
原式=12×(-
)=-5.5 12