3x²-[5x-(x-2)+2x²]其中x= -1/2先化简再求值.

问题描述:

3x²-[5x-(x-2)+2x²]其中x= -1/2
先化简再求值.


原式
=3x²-[5x-x+2+2x²]
=3x²-(4x+2x²+2)
=x²-4x-2
=(-1/2)²-4×(-1/2)-2
=1/4+2-2
=1/4