帮忙数学
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（a+b)²-4a²b²
=(a+b+2ab)(a+b-2ab)
9(2m+n)-4(m-2n)²
=[3(2m+n)-2(m-2n)][3(2m+n)+2(m-2n)]
=(6m+3n-2m+4n)(6m+3n+2m-4n)
=(4m+7n)(9m-n)
x^4-y^4
=(x²-y²)(x²+y²)
=(x-y)(x+y)(x²+y²)
-81+x^4
=(x²-9)(x²+9)
=(x-3)(x+3)(x²+9)
4x²-64
=4(x²-16)
=4(x-4)(x+4)
3a(a+b)²-27ab²
=3a[(a+b)²-9b²]
=3a(a+b-3b)(a+b+3b)
=3a(a-2b)(a+4b)
=(a+b+2ab)(a+b-2ab)
9(2m+n)-4(m-2n)²
=[3(2m+n)-2(m-2n)][3(2m+n)+2(m-2n)]
=(6m+3n-2m+4n)(6m+3n+2m-4n)
=(4m+7n)(9m-n)
x^4-y^4
=(x²-y²)(x²+y²)
=(x-y)(x+y)(x²+y²)
-81+x^4
=(x²-9)(x²+9)
=(x-3)(x+3)(x²+9)
4x²-64
=4(x²-16)
=4(x-4)(x+4)
3a(a+b)²-27ab²
=3a[(a+b)²-9b²]
=3a(a+b-3b)(a+b+3b)
=3a(a-2b)(a+4b)
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