先化简,再求值:3xyz+2(x²y+y²z-xyz)-xyz+2z²x,其中x=1、y=-1、z=2;
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先化简,再求值:3xyz+2(x²y+y²z-xyz)-xyz+2z²x,其中x=1、y=-1、z=2;
先化简,再求值:3xyz+2(x²y+y²z-xyz)-xyz+2z²x,其中x=1、y=-1、z=2;
先化简,再求值:3xyz+2(x²y+y²z-xyz)-xyz+2z²x,其中x=1、y=-1、z=2;
原式=3xyz+2x²y+2y²z-2xyz-xyz+2z²x
=(3xyz-2xyz-xyz)+2x²y+2y²z+2zx²
=2(x²y+y²z+zx²)
=2×[1²×(-1)+(-1)²×2+2²×1]
=2×(-1+2+4)
=2×5
=10
8
=3xyz+(2x²y+2y²z-2xyz)-xyz+2z²x
=3xyz+2x²y+2y²z-2xyz-xyz+2z²x
=2x²y+2y²z+2z²x
当x=1、y=-1、z=2时
-2+4+8
=10