数学简便计算1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?
数学简便计算1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?
1/(1x2x3)+1/(2x3x4)+1/(3x4x5)+.1/(20x21x22)=?
1x2X3+2x3X4+3x4X5+…+7X8X9=?
1/1x2x3与1/2x3x4、1/3x4x5、依此类推以至于1/20x21x22的总和是多少?
1x2x3+2x3x4+3x4x5+…+8x9x10
1x2x3+2x3x4+3x4x5+...+7x8x9=,
1/1x2x3+1/2x3x4+1/3x4x5
1x2x3+2x3x4+3x4x5+.+10x11x12
1x2x3+2x3x4+3x4x5……+10x11x12巧算 请在两天之内回答
1/1x2x3+1/2x3x4+1/3x4x5+1/4x5x6+.+1/48x49x50=
1/1x2x3+1/2x3x4+1/3x4x5+.+1/11x12x13=
1/1x2x3+1/2x3x4+1/3x4x5+.+1/9x10x11=