用求差比较法：为方便起见先扩大2倍
2a^2+2b^2+2-2ab-2a-2b
=a²-2ab+b²+a²-2a+1+b²-2b+1
=(a-b)²+(a-1)²+(b-1)²>=0
所以2a^2+2b^2+2>=2ab+2a+2b
即a^2+b^2+1≥ab+a+b