①a2+b2+2ab=(a+b)2;
②a2+b2-2ab=(a-b)2;
③b2+c2+2bc= (b+c)2;
④b2+c2+ab+bc+ac=(a+b+c)(b+c) ;
⑤(a+b+c)2-(b+c)2=a2 +2ab+2ac;
⑥ (a+b+c)(a+b+c)=a2+b2+c2+ab+bc+ac;
⑦a2+b2+c2+2ab+ 2bc+2ac= (a+b+c)2 .