57*55/56+27*27/28
1/1*2+1/2*3+1/3*4......+1/2007*2008
57*55/56+27*27/28
1/1*2+1/2*3+1/3*4......+1/2007*2008
57*55/56+27*27/28
=(56+1)*(56-1)/56+(28-1)*(28-1)/28
=(56*56-56+56-1)/56+(28*28-28+28+1)/28
=(56*56-1)/56+(28*28+1)/28
=56-1/56+28+1/28
=84+1/56