由[（a-2)/（a（a+2)-（a-1)/（a+2)²]÷（a-4)/（a+2)=[（a-2)(a+2)/a(a+2)²-a(a-1)/a(a+2)²=(a-4)/a(a+2)²×(a+2)/(a-4)=1/a(a+2)∵a²+2a=√3,∴1/a(a+2)=1/(a²+2a)=1/√3=√3/3....