1.a＾2＋b＾2＋5 - 2(2a-b) =(a^2-4a+4)+(b^2+2b+1)=(a-2)^2+(b+1)^2>=0
2. 2*(a＾2＋b＾2＋c＾2)-2*(ab＋bc＋ca )=(a^2-2ab+b^2)+(b^2+2bc+c^2)+(c^2+2ac+a^2)=(a+b)^2+(b+c)^2+(a+c)^2>=0,