(x+y)-(2x+y/2)-(3x+y/6)-(4x+y/12)-(5x+y/20)-……-(10x+y/90)
=x-2x-3x-4x-..-10x+y*(1-1/2-1/6-1/12-..1/90)
=2x-(1+2+..+10)x+y*(1-1/1+1/2-1/2+1/3-..-1/9+1/10)
=2x-10*(1+10)x/2+y*1/10
=2x-55x+y/10
=-53x+y/10