2/5+1/4-1/2 =2/5+1/4-2/4 =8/20+5/20 =13/20 哪里错了

1 2 3 4 5=1 1()2()3()4()5=1 1+1-2+3-4+5=? X=2/5[2/5(1/4X-1)-4又1/2]+4 1+2+3-4-5+1+1+2+3= 4/5×1/4-1/2x=1/20 巧算：(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)===== 1=5 2=1 5 3=2 1 5 4=3 2 1 5 5=? 1+2=3 4+5=? 1/2+1/(2+3)+1/(2+3+4)+.+1/(2+4+5+...)200)=? 1/1*2+1/2*3+1/3*4+1/4*5+.+1/39*40=? 1/1*2+1/2*3+1/3*4+1/4*5+.+1/2004*2005=? 1/1*2+1/2*3+1/3*4+1/4*5+^+1/199*200=? (2*3*4*5)*(1/2+1/3+1/4+1/5)= 5+2+0+1+3+1+4=2+5+0+1+3+1+4 1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+3/5+4/5+...+1/100+2/100+...+99/100=? 1/2+(1/3+2/3)+(1/4+2/4+3/4)+(1/5+2/5+3/5+4/5)+...+(1/60+2/60+.+59/60)=? 判断：1/4+2/5+3/5=1/4+（2/5+3/5）对错