1.a²-25b²
=（a+5b)(a-5b)
2.-1/9+x²/4
=(x/2+1/3)(x/2-1/3)
3.（a+b）²-（a+c）²
=[(a+b)+(a+c)][(a+b)-(a+c)]
=(2a+b+c)(b-c)
4.16（x-y)²-49（x+y）²
=[4(x-y)+7(x+y）][(4（x-y)-7(x+y)]
=(4x-4y+7x+7y)(4x-4y-7x-7y)
=（11x+3y)(-3x-11y)
=-(11x+3y)(3x+11y)
5.m的四次方-n的四次方
=(m^2+n^2)(m^2-n^2)
=(m^2+n^2)(m+n)(m-n)
6.（x-3）（x+12）-9x
=x^2+9x-36-9x
=x^2-36
=(x+6)(x-6)