第一题（x+1）分之1-x+1
=1/(x+1)-(x-1)(x+1)/(x+1)
=(1-x²+1)/(x+1)
=(2-x²)/(x+1)
第二题【（ab）分之（a+b）+2】+（a-b）分之（a²-b²）
=(a+b)/ab+2+(a+b)(a-b)/(a-b)
=(a+b)/ab+2+a+b
=(a+b+2ab+a²b+ab²)/ab
4、(a+1)²/(a+1)(a-1)-1/(a-1)
=(a+1)/(a-1)-1/(a-1)
=a/(a-1)