（7x^2-y^2)^2-(x^2-7y^2)^2急

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（7x^2-y^2)^2-(x^2-7y^2)^2急（7x^2-y^2)^2-(x^2-7y^2)^2急（7x^2-y^2)^2-(x^2-7y^2)^2急原式=[(7x^2-y^2)+(x^2-7y

（7x^2-y^2)^2-(x^2-7y^2)^2急
（7x^2-y^2)^2-(x^2-7y^2)^2
急

（7x^2-y^2)^2-(x^2-7y^2)^2急
原式=[(7x^2-y^2)+(x^2-7y^2)][(7x^2-y^2)-(x^2-7y^2)]
=(7x^2-y^2+x^2-7y^2)(7x^2-y^2-x^2+7y^2)
=(8x^2-8y^2)(6x^2+6y^2)
=48(x+y)(x-y)(x^2+y^2)

（7x^2-y^2)^2-(x^2-7y^2)^2
=（7x^2-y^2+x^2-7y^2)(7x^2-y^2-x^2+7y^2)
=48(x^2-y^2)(x^2+y^2)
=48(x+y)(x-y)(x^2+y^2)

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