Question

先化简再求值:3x^2-[1/2x^2y-(2xy+2x^2-x^y)-(2x^2y+xy)],

中x=1,y=-2

Answer 1

3x^2-[1/2x^2y-(2xy+2x^2-x^y)-(2x^2y+xy)],
=3x²-x²y/2+2xy+2x²-x²y+2x²y+xy
=5x²+x²y/2+3xy
=5×1²+1²×(-2)/2+3×1×(-2)
=5-1-6
=-2;

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Answer 2

3x^2-[1/2x^2y-(2xy+2x^2-x^y)-(2x^2y+xy)]
=1/2 (10 x^2 - 2 x^y + 6 x y + 3 x^2 y)
=1/2 (10 - 2 + 6 (-2) + 3 (-2))
=-5