第1个回答 2011-07-24
1/2+1/6+1/12+1/20+1/30+1/42=1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7=6/7
2+4+6+...+2010=2*{[(1+1005)*1005]/2}=1005*1006=(1000+5)*1006=1006000+5030=1011030
(5/9-5/6+1/4)÷(-1/36)=(5/9-5/6+1/4)*(-36)=-(20-30+9)=1
(-19 18/19)*38=-(19*38+18/19*38)=-(19²*2+18*2)=-[(20-1)²*2+36]
=-[(400-40+1)*2+36]=-(361*2+36)=-(722+36)=-758