初一都不会做的幼稚的数学题

1/2-1/6-1/12-1/20-1/30-1/42
=1/2-(1/6+1/12+1/20+1/30+1/42)
=1/2-[1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)]
=1/2-(1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=1/2-(1/2-1/7)
=1/2-1/2+1/7
=1/7
貌似。。。貌似而已～

原式=1/(1x2)- 1/(2x3)- 1/(3x4)- 1/(4x5)- 1/(5x6)- 1/(6x7)

1/(1x2)=1-1/2 1/(2x3)=1/2-1/3 1/(3x4)=1/3-1/4
1/(4x5)=1/4-1/5 1/(5x6)=1/5-1/6 1/(6x7)=1/6-1/7

所以=(1-1/2)-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-(1/5-1/6)-(1/6-1/7)

去括号 得：1-1/7=6/7

1/2－1/6－1/12－1/20－1/30－1/42
＝1/(1×2)-1/(2×3)-1/(3×4)-1/(4×5)-1/(5×6)-1/(6×7)
＝1/2-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-(1/5-1/6)-(1/6-1/7)
＝1/2-1/2+1/3-1/3+1/4-1/4+1/5-1/5+1/6-1/6+1/7
＝1/7

1/2-1/6-1/12-1/20-1/30-1/42
=1/1x2-1/2x3-1/3x4-1/4x5-1/5x6-1/6x7
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
对不起,乘号用了x代替.