2? 2a+b a+b ÷ 4a2+4ab+b2 a2?b2 =2- 2a+b a+b ? (a+b)(a?b) (2a+b)2 =2- a?b 2a+b = 4a+2b?a+b 2a+b = 3(a+b) 2a+b ，当a=-1，b= 1 2 时，原式= 3(?1+ 1 2 ) ?2+ 1 2 =1．
