(2a)/(a的平方-4)+(1)/(2-a)-1 =2a/(a+2)(a-2)-1/(a-2)-1 =2a/(a+2)(a-2)-(a+2)/(a+2)(a-2)-(a+2)(a-2)/(a+2)(a-2) =(a-2)[1-(a+2)]/(a+2)(a-2) =-(a+1)/(a+2)
