(1 ) (1-2)*(2-3)*(3-4)*.*(99-100) =(-1)*(-1)*……(-1)括号的左边从1到99,所以有99个括号99是奇数,有奇数个(-1)相乘所以=-1(2) 1/(10*11)+1/(11*12)+.+1/(19*20)+1/(20*21) =(1/10-1/11)+(1/11-1/12)+.+1+(1/19-1/...