c/ 1/1.3+ 1/3.5+1/5.7+1/7.9+ 1/9.11
d/ 2/1.3+2/3.5+ 2/5.7+ 2/7.9+ 2/9.11
e/ (1+1/2).(1+1/3).(1+1/4)…(1+1/100)
f / (1-1/2).(1-1/3).(1-1/4)…(1-1/100)
c/ 1/1.3+ 1/3.5+1/5.7+1/7.9+ 1/9.11
d/ 2/1.3+2/3.5+ 2/5.7+ 2/7.9+ 2/9.11
e/ (1+1/2).(1+1/3).(1+1/4)…(1+1/100)
f / (1-1/2).(1-1/3).(1-1/4)…(1-1/100)
Mình chỉ giải được câu c và d thôi mong bạn thông cảm.
c) $\frac{1}{1.3}$ + $\frac{1}{3.5}$ + $\frac{1}{5.7}$ + $\frac{1}{7.9}$ + $\frac{1}{9.11}$
⇔ $\frac{1}{2}$.($\frac{2}{1.3}$ + $\frac{2}{3.5}$ + $\frac{2}{5.7}$ + $\frac{2}{7.9}$ + $\frac{2}{9.11}$ )
⇔ $\frac{1}{2}$.($\frac{1}{1}$ – $\frac{1}{3}$ + $\frac{1}{3}$ – $\frac{1}{5}$ + $\frac{1}{5}$ – $\frac{1}{7}$ + $\frac{1}{7}$ – $\frac{1}{9}$ + $\frac{1}{9}$ – $\frac{1}{11}$
⇒$\frac{1}{2}$.(1 – $\frac{1}{11}$)
⇒$\frac{1}{2}$.$\frac{10}{11}$ = $\frac{5}{11}$
d) 2/1.3+2/3.5+ 2/5.7+ 2/7.9+ 2/9.11
<=>1/1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11
=> 1 – 1/11 = 10/11
#Chucbanhoctot
Đáp án:
c,`1/(1.3)+1/(3.5)+1/(5.7)+1/(7.9)+1/(9.11)`
`=1/2. (2/(1.3)+2/(3.5)+2/(5.7)+2/(7.9)+2/(9.11))`
`=1/2.(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)`
`=1/2.(1-1/11)`
`=1/2 . 10/11=5/11`
d,`2/(1.3)+2/(3.5)+2/(5.7)+2/(7.9)+2/(9.11)`
`=1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11`
`=1-1/11`
`=10/11`
e,`(1+1/2).(1+ 1/3). ( 1+1/4)…(1+ 1/100)`
`=3/2 . 4/3 . 5/4 ……………. 101/100`
`=(3.4.5….101)/(2.3.4…..100)`
`=101/2`
f/ `( 1-1/2). ( 1-1/3).( 1-1/4) …(1-1/100)`
`=1/2 . 2/3 . 3/4 ……….. 99/100`
`=(1.2.3…99)/(2.3.4….100)`
`=1/100`
XIN HAY NHẤT NHA
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