1/3-1/2=-4/3?应该是1/3-1/2=-1/6,2/5-2/3=-4/15,3/8-3/5=-9/40,4/11-4/7=-16/77,5/14-5/9=-25/126,第六个是：6/17-6/11=-36/187
n不等于1时 ,规律是：n/(3n-1) - n/(2n-1) = -(n^2)/(3n-1)(2n-1)2/3-2/1=-4/3,3/8-3/5=9/40,4/11-4/7=-16/77,5/14-5/9=-25/126,请写出这列算式中的第6个算式是什么?7/20 - 7/13 = - 49/260