已知a,b为实数,且ab=3,a+b=4,通分（a-1）/（a+1）,（b-1）/（b+1）试求（a-1）/（a+1）的值我已经会了，等于0或1/2

Question

已知a,b为实数,且ab=3,a+b=4,
通分（a-1）/（a+1）,（b-1）/（b+1）
试求（a-1）/（a+1）的值
我已经会了，等于0或1/2

Answer 1

(a+1)(b+1)=ab+(a+b)+1=8
(a-1)(b-1)=ab-(a+b)+1=0,得到a=1,b=3或者a=3,b=1
(a-1)/(a+1)=(a-1)(b+1)/(a+1)(b+1)=(a-1)(b+1)/8
同理(b-1）/（b+1）=(b-1)(a+1)/8
则（a-1）/（a+1）=0或者0.5