Ответ:\[2x^2+7xy-5x^2-11xy+3y^2=-3x^2-4xy+3y^2.\]\[(x^2+3x+4)(x^2-3x-4)=x^4-(3x+4)^2=x^4-9x^2-24x-16.\]\[x(x^2+x)-x(x^2+x)=0.\]\[-5x^2(x-8)+10x^2=-5x^3+40x^2+10x^2=-5x^3+50x^2.\]\[(x^2+2y)(x^2-2y)-(x^2+2y)(x^2-2y)=0.\]