6) -x^2-2xy-1=-((x^2+2xy+y^2-y^2+1))=-((x+y)^2-(y^2-1))=?
7)1-a^2-2ab-b^2=1-(a^2+2ab+b^2)=1-(a+b)^2=(1-a-b)(1+a+b)
8)(x-y)z^2+2z(x-y)+(x-y)=(x-y)(z^2+2z+1)=(x-y)(z+1)^2
9)m(m+n)+n(m+n)-9m^2=(m+n)(m+n)-9m^2=((m+n)^2-9m^2=
=(m+n-3m)(m+n-3m)
10) (x-2)^2-(x+3)^2=5
(x-2-x-3)(x-2+x+3)=5
-5(2x+1)=5
x+1=-1; x=-2 11)8-a^3=2^3-a^3=(2-a)(4+2a+a^2)
12) x^3-(x-3)^3=9x^2
(x-x+3)(x^2+x(x-3)+(x-3)^2)=9x^2
3(x^2+x^2-3x+x^2-6x+9)=9x^2 | :3
3x^2-9x+9=3x^2
-9x=-9; x=1