原式
2(a+1) (a-2)² a+1
=------------- + ------------- × -----------
(a+1)(a-1) a²-1 a-2
2(a+1) a-2
=------------- + -------------
a²-1 a-1
2(a+1)+(a-2)(a+1)
=----------------------------
a²-1
2a+2+a²-a-2
=----------------------------
a²-1
a(a+1)
=----------------------------
a²-1
a
=---------
a-1
1+√2
=-----------
√2
=(√2+2)/2