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\(\frac{1}{9\cdot10}+\frac{2}{10\cdot12}+\frac{3}{12\cdot15}+\frac{4}{15\cdot19}+\frac{5}{19\cdot24}+\frac{6}{24\cdot30}
\)
\(=\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{15}+\frac{1}{15}-\frac{1}{19}+\frac{1}{19}-\frac{1}{24}+\frac{1}{24}-\frac{1}{30}\)
\(=\frac{1}{9}-\frac{1}{30}\)
\(=\frac{10}{90}-\frac{3}{90}\)
\(=\frac{7}{90}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
A) \(\frac{7}{8}-\frac{5}{12}=\frac{84}{96}-\frac{40}{96}=\frac{44}{96}=\frac{11}{24}\)
B)\(\frac{8}{15}-\frac{2}{5}=\frac{8}{15}-\frac{6}{15}=\frac{2}{15}\)
C)\(\frac{5}{6}-\frac{3}{10}=\frac{50}{60}-\frac{18}{60}=\frac{32}{60}=\frac{8}{15}\)
D)\(\frac{7}{10}-\frac{1}{5}=\frac{7}{10}-\frac{2}{10}=\frac{5}{10}=\frac{1}{2}\)
2)A)\(\frac{5}{10}-\frac{2}{15}=\frac{1}{2}-\frac{2}{15}=\frac{15}{30}-\frac{4}{30}=\frac{11}{30}\)
B)\(\frac{5}{20}-\frac{1}{6}=\frac{1}{4}-\frac{1}{6}=\frac{6}{24}-\frac{4}{24}=\frac{2}{24}=\frac{1}{12}\)
C)\(\frac{6}{18}-\frac{6}{24}=\frac{1}{3}-\frac{1}{4}=\frac{4}{12}-\frac{3}{12}=\frac{1}{12}\)
D)\(\frac{5}{9}-\frac{3}{12}=\frac{5}{9}-\frac{1}{4}=\frac{20}{36}-\frac{9}{36}=\frac{11}{36}\)
Chúc bạn học tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
A) \(\dfrac{5}{10}-\dfrac{2}{15}\)
\(=\dfrac{1}{2}-\dfrac{2}{15}\)
\(=\dfrac{15}{30}-\dfrac{4}{30}\)
\(=\dfrac{11}{30}\)
B)\(\dfrac{5}{20}-\dfrac{1}{6}\)
\(=\dfrac{1}{4}-\dfrac{1}{6}\)
\(=\dfrac{6}{24}-\dfrac{4}{24}\)
\(=\dfrac{2}{24}=\dfrac{1}{12}\)
C) \(\dfrac{6}{18}-\dfrac{6}{24}\)
\(=\dfrac{1}{3}-\dfrac{1}{4}\)
\(=\dfrac{4}{12}-\dfrac{3}{12}\)
\(=\dfrac{1}{12}\)
D) \(\dfrac{5}{9}-\dfrac{3}{12}\)
\(=\dfrac{5}{9}-\dfrac{1}{4}\)
\(=\dfrac{20}{36}-\dfrac{9}{36}\)
\(=\dfrac{11}{36}\).
a: =1/2-2/15
=15/30-4/30
=11/30
b: =1/4-1/6
=3/12-2/12
=1/12
c: =1/3-1/4
=1/12
d: =20/36-9/36
=11/36
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a và d là hai phương án sai
vì 28-12:8=28-1,5=26,5>4
và 24:2,3>4
\(\dfrac{3}{2}xD=1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+...+\dfrac{1}{256}\)
Đặt
\(A=1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+...+\dfrac{1}{256}\)
\(2xA=2+1+\dfrac{1}{2}+\dfrac{1}{4}+...+\dfrac{1}{128}\)
\(A=2xA-A=2-\dfrac{1}{256}=\dfrac{511}{256}=\dfrac{3}{2}xD\)
\(\Rightarrow D=\dfrac{511}{256}:\dfrac{3}{2}\)