先化简a+1分之1-a²-2a+1分之a+1除以a-1分之a+1,然后从-1.1.根2中选一个作为a的值带入求值

[ 1/(a+1) - (a+1)/(a²-2a+1) ] ÷ (a+1)/(a-1)= [ 1/(a+1) - (a+1)/(a-1)² ] × (a-1)/(a+1)= [ (a-1)² - (a+1)² ] / [ (a+1)(a-1)² ] × (a-1)/(a+1)= - 4a / [ (a+1)² (a-1) ]a只...