Đáp án + Giải thích các bước giải:
c, `1/3 - 3/4 + 3/5 + 1/2007 - 1/36 + 1/15 - 2/9`
` = (1/3 + 3/5 + 1/15) - (3/4 + 1/36 + 2/9) + 1/2007`
` = ( 5/15 + 9/15 + 1/15) - ( 27/36 + 1/36 + 8/36) + 1/2007`
` = 15/15 - 36/36 + 1/2007`
` = 1 - 1 + 1/2007`
` = 0 + 1/2007`
` = 1/2007`
d, `1/(1.2) + 1/(2.3) + 1/(3.4) + ... + 1/(2006.2007)`
` = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/2006 - 1/2007`
` = 1 - 1/2007`
` = 2007/2007 - 1/2007`
` = 2006/2007`
