=3(2x-y)^2-4(x+2y)^2
= 3(2x-y)-4(x+2y)* 3(2x-y)+4(x+2y
=(2x- 1 1y)( 10x+5y)
12 1(a-b)^2- 169(a+b)^2
= 1 1(a-b)^2- 13(a+b)^2
= 1 1(a-b)- 13(a+b)* 1 1(a-b)+ 13(a+b)
=-4(a+ 12b)( 12a+b)
3 n^2(m-2)-n(2-m)
=n^2(m-2)+n(m-2)
=(m-2)n(n+ 1)
4 (x^2-2x)^2-2x(2-x)+ 1
=x(x-2)^2+2x(x-2)+ 1
=x(x-2)+ 1^2
=(x- 1)^4