Помогите срочно!!6 номер!!
=2a^2+2ab-2ac-(2ab-2b^2-2bc)+2ac-2bc+2c^2=2a^2+2ab-2ac-2ab+2b^2+2bc+2ac-2bc+2c^2=2a^2+2b^2+2c^2=2 (a^2+b^2+c^2)