求做2道因式分解
问题描述：
求做2道因式分解
25x^2-(4x-3y)^2
m^4-18m^2n^2+81n^4
答
25x^2-(4x-3y)^2
=[5x+(4x-3y)][5x-(4x-3y)]
=(5x+4x-3y)(5x-4x+3y)
=(9x-3y)(x+3y)
=3(3x-y)(x+3y)
m^4-18m^2n^2+81n^4
=(m^2-9n^2)^2
=(m+3n)^2(m-3n)^2
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