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

5x(x2-2x+4)-x2(5x-2)+(-4x)(2-2x)
=5x3-10x2+20x-5x3+2x2-8x+8x2
=12x,
当x=-

5
12
时,
原式=12×(-
5
12
)=-5.