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5454/5757=18/19
171717/191919=17/19
18/19-17/19=1/19
![](https://rs.olm.vn/images/avt/0.png?1311)
a,2/3 * 3/4 * 4/5 * 5/6
Giản ước 3 với 3 , 4 với 4 , 5 với 5
=>2/3 * 3/4 * 4/5 * 5/6=2/6=1/3
b,5454/5757-171717/191919
=54/57-17/19
Quy đồng:54/57-(17*3/19*3)
=54/57-51/57
=3/57=1/19
NHỚ CLICK ĐÚNG CHO MÌNH NHA!!!!
a,2/3 * 3/4 * 4/5 * 5/6
Giản ước 3 với 3 , 4 với 4 , 5 với 5
=>2/3 * 3/4 * 4/5 * 5/6=2/6=1/3
b,5454/5757-171717/191919
=54/57-17/19
Quy đồng:54/57-(17*3/19*3)
=54/57-51/57
=3/57=1/19
![](https://rs.olm.vn/images/avt/0.png?1311)
1) a) \(\frac{5454}{5757}-\frac{171717}{191919}=\frac{18\times3\times101}{19\times3\times101}-\frac{17\times10101}{19\times10101}=\frac{18}{19}-\frac{17}{19}=\frac{1}{19}\)
b) \(\frac{6}{5}\times\frac{7}{6}\times\frac{8}{7}\times....\times\frac{2021}{2020}=\frac{6\times7\times8\times...\times2021}{5\times6\times7\times...\times2020}=\frac{2021}{5}\)
2) \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{45}=2\times\frac{1}{6}+2\times\frac{1}{12}+2\times\frac{1}{20}+...+2\times\frac{1}{90}\)
\(=2\times\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)
\(=2\times\left(\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+...+\frac{1}{9\times10}\right)\)
\(=2\times\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\right)=2\times\left(\frac{1}{2}-\frac{1}{10}\right)=2\times\frac{2}{5}=\frac{4}{5}\)
b)Vì \(a-1< a+1\)
=> \(\frac{1}{a-1}>\frac{1}{a+1}\)
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27 x \(\left(\frac{171717}{272727}+\frac{373737}{363636}\right)\)
= 27 x \(\left(\frac{17}{27}+\frac{37}{36}\right)\)
= 27 x \(\frac{17}{27}\)+ 27 x \(\frac{37}{36}\)
= 17 + 27,75
= 44,75
![](https://rs.olm.vn/images/avt/0.png?1311)
1717/1919=17/19
171717/191919=17/19
Vậy 1717/1919 = 171717/191919
![](https://rs.olm.vn/images/avt/0.png?1311)
1717/1919 = 17.101/19.101
171717/191919 = 17.10101/19.10101
→ 17/19 = 1717/1919 = 171717/191919
Ta thay : 17/19 = 17x1/19x1
1717/1919 = 17x101/19x101
171717/191919 = 17x10101/19x10101
Nen 17/19 = 1717/1919 = 171717/191919.
Nho k minh nha!
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(15\times\left(\frac{212121}{434343}+\frac{333333}{353535}\right)=15\times\left(\frac{21\times10101}{43\times10101}+\frac{33\times10101}{35\times10101}\right)\)
\(=15\times\left(\frac{21}{43}+\frac{33}{35}\right)=\frac{6462}{301}\)
b) \(\frac{639\times721721}{721\times639639}=\frac{639\times721\times1001}{721\times639\times1001}=1\)
c) \(\frac{327\times412+400}{328\times412-12}=\frac{\left(328-1\right)\times412+400}{328\times412-12}=\frac{328\times412-412+400}{328\times412-12}\)
\(=\frac{328\times412-12}{328\times412-12}=1\)
d) \(9\times\left(\frac{151515}{171717}+\frac{131313}{181818}\right)=9\times\left(\frac{15\times10101}{17\times10101}+\frac{13\times10101}{18\times10101}\right)=9\times\left(\frac{15}{17}+\frac{13}{18}\right)\)
\(=9\times\frac{491}{306}=\frac{491}{34}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{3636}{3535}+\frac{5454}{4242}\)
\(=\frac{36}{35}+\frac{54}{42}\)
= \(\frac{36}{35}+\frac{9}{7}\)
= \(\frac{36}{35}+\frac{45}{35}\)
= \(\frac{81}{35}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{191919}{373737}=\frac{191919:10101}{373737:10101}=\frac{19}{37}\)
\(\frac{5454}{5757}-\frac{171717}{191919}=\frac{18.303}{19.303}-\frac{17.10101}{19.10101}=\frac{18}{19}-\frac{17}{19}=\frac{1}{19}\)
Ta có :
\(\frac{5454}{5757}=\frac{54.101}{57.101}=\frac{54}{57}\); \(\frac{171717}{191919}=\frac{17.10101}{19.10101}=\frac{17}{19}\)
Vậy \(\frac{54}{57}-\frac{17}{19}=\frac{1}{19}\)