原式=x²-2[1/2x²-(x+5+2x²-12)+4x²]
=x²-2(1/2x²-x-5-2x²+12+4x²)
=x²-x²+2x+10+4x²-24-8x²
=(x²-x²+4x²-8x²)+2x+(10-24)
=-4x²+2x-14
当x=-2时
原式=-4×(-2)²+2×(-2)-14
=-4×4-4-14
=-16-18
=-34