举报
心巧手拙虫细细
=19 931 992^2/((19 931 991+19 931 993)^2-2*19 931 991*19 931 993-2) =19 931 992^2/(2*19 931 992)^2-2(19 931 992+1)(19 931 992-1)-2) =19 931 992^2/(4*19 931 992^2-2(19 931 992+1)(19 931 992-1)-2) =19 931 992^2/(4*19 931 992^2-2*19 931 992^2) =1/(4-2) =1/2 增加一步能否明白?