\(\frac{2}{4}+\frac{2}{28}+\frac{2}{70}+\frac{2}{130}+\frac{2}{208}\)

= \(\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}\)

= \(\frac{2}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{13.16}\right)\)

= \(\frac{2}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\right)\)

= \(\frac{2}{3}.\left(1-\frac{1}{16}\right)\)

= \(\frac{2}{3}.\frac{15}{16}\)

= \(\frac{5}{8}\)

2/4 + 2/28 + 2/70 + 2/130 + 2/208

= 2/1.4 + 2/4.7 + 1/7.10 + 1/10.13 + 1/13.16

= 2/3.(1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + 1/13 - 1/16)

= 2/3.(1 - 1/16)

= 2/3.15/16

= 5/8

P/s: "." là nhân nhé :V

X = 3/4 + 3/28 + 3/70 + .... + 3/208

X = 3/1.4 + 3/4.7 + 3/7.10 + ... + 3/13.16

X = 1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + .... + 1/13 - 1/16

X = 1 - 1/16

X = 15/16

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3/2  ..>.   2/3

15/6 .=.. 5/2

4/3 ..>. 5/7

8/9 .<.. 1

A=\(\frac{1}{3}\)+\(\frac{1}{8}\)+\(\frac{1}{15}\)+\(\frac{1}{24}\)+\(\frac{1}{35}\)+\(\frac{1}{48}\)+\(\frac{1}{63}\)+\(\frac{1}{80}\)

A=\(\frac{1}{2}\)(\(\frac{1}{1\cdot3}\)+\(\frac{1}{2\cdot4}\)+\(\frac{1}{3\cdot5}\)+\(\frac{1}{4.6}\)+\(\frac{1}{5.7}\)+\(\frac{1}{6.8}\)+\(\frac{1}{7.9}\)+\(\frac{2}{8.10}\))

A=\(\frac{1}{2}\)(1-1/3 +1/2-1/4 + 1/3 -1/5 +1/4-1/6 +1/5 - 1/7 +1/6 -1/8 +1/7 - 1/9 +1/8 - 1/10)

A= \(\frac{1}{2}\)(1 + 1/2 -1/9 -1/10)

A=\(\frac{29}{45}\)

a)1/7=2/14=3/21=4/28=5/35=6/42=7/49=8/56=...

70/700=1/10=2/20=3/30=4/40=5/50=6/60=7/70=...

b)1/3<3/8<5/12<4/9<1/2

c)1/4<13/48<7/24<5/16<1/3

k cho mik nha

Giúp mình điii

\(\dfrac{18}{24}\)và\(\dfrac{3}{4}\)

\(\dfrac{18}{24}=\dfrac{18:6}{24:6}\)\(=\dfrac{3}{4}\)

\(\dfrac{3}{4}=\dfrac{3}{4}\)

Vậy\(\dfrac{18}{24}=\dfrac{3}{4}\)

a)  2 tấn 3 tạ 5kg  = 2035kg         b)  3 tấn 32 yến  <  3032 yến

c)  7 năm > 70 tháng                  d)  2 thế kỷ 8 năm  = 208 năm

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Tính nhanh :

\(a.1+2+3+...+98+99+100\)

\(=\left(100+1\right).100:2\)

\(=101.100:2\)

\(=10100:2\)

\(=5050\)

\(b.16.48+8.48+16.28\)

\(=48.\left(16+8\right)+16.28\)

\(=48.24+16.28\)

\(=1152+448\)

\(=1600\)