1.49-x^2=(7+x)(7-x)
2.4x^2-169y^2=(2x+13y)(2x-13y)
3.-1+25a^2=(5a+1)(5a-1)
4.0.01m^2-625n^2=(0.1m+25n)(0.1m-25n)
5.x^2-9y^2=(x+3y)(x-3y)
6.16m^2-9n^2=(4m+3n)(4m-3n)
7.-4x^2+1=(1+2x)(1-2x)
8.25(a+b)^2-9a^2b^2=(5(a+b)+3ab)(5(a+b)-3ab)
9.(a+2b)^2+6(a+2b)+9=(a+2b+3)^2
10.x^3y+2x^2y^2+xy^3=xy(x^2+2xy+y^2)=xy(x+y)^2
11.1/2x^2y^2+2xy+2=(x^2y^2+4xy+4)/2=(xy+2)^2/2