Đáp án:
`↓↓↓`
Giải thích các bước giải:
`a) A = 1/(5.6)+1/(6.7)+...+1/(24.25)`
`= 1/5-1/6+1/6-1/7+....+1/24-1/25`
`= 1/5-1/25=4/25`
`b) B = 2/(1.3)+2/(3.5)+....+2/( 99.101)`
`= 1/1-1/3+1/3-1/5+....+1/99-1/101`
`= 1/1-1/101=100/101`
`c) C = 5^2/(1.6)+5^2/(6.11)+....+5^2/(26.31)`
`= 5.(5/(1.6)+5/(6.11)+...+5/(26.31))`
`= 5.(1/1-1/6+1/6-1/11+...+1/26-1/31)`
`= 5.(1/1-1/31) = 5 . 30/31 = 150/31`
`d) D = 4/(11.16)+4/(16.21)+....+4/(61.66)`
`= 4/5 .(5/(11.16)+5/(16.21)+....+5/(61.66))`
`= 4/5 .(1/11-1/16+1/16-1/21+....+1/61-1/66)`
`= 4/5 . (1/11-1/66) = 4/5 . 5/66 = 2/33`
