(3x^2-4y^2)+[-(x^2-2xy-y^2)]-[-(3x^2-2xy-y^2)]
=3x^2-4y^2-(x^2-2xy-y^2)+(3x^2-2xy-y^2)
=3x^2-4y^2-x^2+2xy+y^2+3x^2-2xy-y^2
=5x^2-4y^2
(3x^2-4y^2)+[-(x^2-2xy-y^2)]-[-(3x^2-2xy-y^2)]
(3x^2-4y^2)+[-(x^2-2xy-y^2)]-[-(3x^2-2xy-y^2)]
数学人气：481 ℃时间：2019-12-09 01:19:30
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