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-5(xy - 2x^2 ) + (5xy - x^2) - 2(3x^2 - 5xy)
= -5xy + 10x^2 + 5xy - x^2 - 6x^2 + 10xy
= (10x^2 - x^2 - 6x^2 ) + ( -5xy + 5xy + 10xy)
= 3x^2 + 10xy
当x = -2, y = -1时，原式= -2×（-2)^2 + 10×(-2)×(-1) = -8 + 20 = 12
= -5xy + 10x^2 + 5xy - x^2 - 6x^2 + 10xy
= (10x^2 - x^2 - 6x^2 ) + ( -5xy + 5xy + 10xy)
= 3x^2 + 10xy
当x = -2, y = -1时，原式= -2×（-2)^2 + 10×(-2)×(-1) = -8 + 20 = 12
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