Đáp án:
`C = 3/(4.7) + 3/(7.10) +... + 3/(73.76)`
`C=1/4-1/7+1/7-1/10+....+1/73-1/76`
`C=1/4-1/76=19/76-1/76=9/38`
Vậy `C=9/38`
`D = 1/(3.5) + 1/(5.7) +...+ 1/(97.99)`
`2D=2.( 1/(3.5) + 1/(5.7) +...+ 1/(97.99))`
`2D=2/(3.5)+2/(5.7)+....+2/(97.99)`
`2D=1/3-1/5+1/5-1/7+.....+1/97-1/99`
`2D=1/3-1/99=32/99`
`D=32/99 . 1/2=16/99`
Vậy `D=16/99`
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