化简:a减1分之1-a加1分之1的差除以2a²减2分之a

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