（1）原式=1-7+3×1+ 1 2 =1-7+3+ 1 2 =- 5 2 ；（2）原式= x+1 x ÷ 2x2?1?x2 2x = x+1 x ? 2x (x+1)(x?1) = 2 x?1 ，当x=3时，原式= 2 3?1 =1．
