
(x+y)^4+(x^2-y^2)^2+(x-y)^4 因式分解,一定要换元法,即设x+y=a,x-y=b
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设x+y=a,x-y=b
(x+y)^4+(x^2-y^2)^2+(x-y)^4
=a^4+(ab)^2+b^4
=(a^4+2a^2b^2+b^4)-a^2b^2
=(a^2+b^2)^2-(ab)^2
=(a^2+b^2-ab)(a^2+b^2+ab)
=(x^2+y^2+2xy+x^2+y^2-2xy-x^2+y^2)(x^2+y^2+2xy+x^2+y^2-2xy+x^2-y^2)
=(x^2+3y^2)(3x^2+y^2)
(x+y)^4+(x^2-y^2)^2+(x-y)^4
=a^4+(ab)^2+b^4
=(a^4+2a^2b^2+b^4)-a^2b^2
=(a^2+b^2)^2-(ab)^2
=(a^2+b^2-ab)(a^2+b^2+ab)
=(x^2+y^2+2xy+x^2+y^2-2xy-x^2+y^2)(x^2+y^2+2xy+x^2+y^2-2xy+x^2-y^2)
=(x^2+3y^2)(3x^2+y^2)
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