Ответ:\((x-3)^2-8=x^2-6x+1\);\(12x-(x+6)^2=12x-(x^2+12x+36)=-x^2-36\);\((2a-3b)^2-4a(a-6b)=4a^2-12ab+9b^2-4a^2+24ab=12ab+9b^2\);\((2x-3y)^2+(4x+2y)^2=20x^2+4xy+13y^2\);\((x-5)^2-x(x+3)=x^2-10x+25-x^2-3x=25-13x\).