1/1x2x3+1/2x3x4+……+1/n(n+1)(n+2)
=1/2x[(1/1x2-1/2x3)+(1/2x3-1/3x4)+……+1/n(n+1)-1/(n+1)(n+2)]
=1/2x[1/2-1/(n²+3n+2)]
=(n²+3n)/4(n²+3n+2)
擦 算了半天数学第一道题没算出来 晕 就是59页的试一试,
1/1x2x3+1/2x3x4+……+1/n(n+1)(n+2)
=1/2x[(1/1x2-1/2x3)+(1/2x3-1/3x4)+……+1/n(n+1)-1/(n+1)(n+2)]
=1/2x[1/2-1/(n²+3n+2)]
=(n²+3n)/4(n²+3n+2)