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A,17/12+9/7-2/7+7/12=(17/12+7/12)+(9/7-2/7)=24/12+7/7=2+1=3
B,9/8-(17/7-3/7)+7/8=(9/8+7/8)-14/7=16/8-14/7=2-2=0
Nhớ k nha
a, 17/12+9/7-2/7+7/12
=(17/12+7/12)+(9/7-2/7)
=24/12+7/7
=2+1
=3
b, 9/8-(17/7-3/7)+7/8
=9/8-14/7+7/8
=(9/8+7/8)-14/7
=16/8-14/7
=2-2
=0
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(\dfrac{7}{8}\) \(\times\) \(\dfrac{3}{13}\) + \(\dfrac{4}{9}\) \(\times\) \(\dfrac{4}{13}\)
= \(\dfrac{1}{13}\) \(\times\)( \(\dfrac{21}{8}\) + \(\dfrac{16}{9}\))
= \(\dfrac{1}{13}\) \(\times\)( \(\dfrac{189}{72}\) + \(\dfrac{128}{72}\))
= \(\dfrac{1}{13}\) \(\times\) \(\dfrac{317}{73}\)
= \(\dfrac{317}{949}\)
b, \(\dfrac{6}{5}\) + \(\dfrac{7}{3}\) + \(\dfrac{8}{9}\)
= \(\dfrac{54}{45}\) + \(\dfrac{105}{45}\) + \(\dfrac{40}{45}\)
= \(\dfrac{199}{45}\)
c, 23 : \(\dfrac{5}{14}\) + \(\dfrac{6}{7}\) + \(\dfrac{4}{9}\)
= \(\dfrac{322}{5}\) + \(\dfrac{6}{7}\) + \(\dfrac{4}{9}\)
= \(\dfrac{20286}{315}\) + \(\dfrac{270}{315}\) + \(\dfrac{140}{315}\)
= \(\dfrac{20696}{315}\)
d, 4\(\dfrac{1}{4}\) + 7\(\dfrac{3}{7}\) - 2\(\dfrac{4}{17}\)
= 4 + \(\dfrac{1}{4}\) + 7 + \(\dfrac{3}{7}\) - 2 - \(\dfrac{4}{17}\)
= (4+7-2) + (\(\dfrac{1}{4}\) + \(\dfrac{3}{7}\) - \(\dfrac{4}{17}\))
= 9 + \(\dfrac{119}{476}\) + \(\dfrac{204}{476}\) - \(\dfrac{112}{476}\)
= 9\(\dfrac{211}{476}\) = \(\dfrac{4495}{476}\)
e, 8 - (9\(\dfrac{2}{11}\) + \(\dfrac{8}{33}\))
= 8 - 9 - \(\dfrac{2}{11}\) - \(\dfrac{8}{33}\)
= -1 - \(\dfrac{2}{11}\) - \(\dfrac{8}{33}\)
= \(\dfrac{-33}{33}\) - \(\dfrac{-6}{33}\) - \(\dfrac{8}{33}\)
= - \(\dfrac{47}{33}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{3}+\frac{3}{7}+\frac{5}{3}+\frac{8}{14}\)
\(=\left(\frac{1}{3}+\frac{5}{3}\right)+\left(\frac{3}{7}+\frac{8}{14}\right)\)
\(=\frac{6}{3}+\left(\frac{6}{14}+\frac{8}{14}\right)\)
\(=2+\frac{14}{14}\)
\(=2+1\)
\(=3\)
\(\frac{5}{6}+\frac{4}{15}+\frac{6}{18}+\frac{3}{45}\)
\(=\left(\frac{5}{6}+\frac{6}{18}\right)+\left(\frac{4}{15}+\frac{3}{45}\right)\)
\(=\left(\frac{5}{6}+\frac{2}{6}\right)+\left(\frac{4}{15}+\frac{1}{15}\right)\)
\(=\frac{7}{6}+\frac{5}{15}\)
\(=\frac{7}{6}+\frac{1}{3}\)
\(=\frac{7}{6}+\frac{2}{6}\)
\(=\frac{9}{6}\)
\(=\frac{3}{2}\)
~ Ủng hộ nhé
\(9\times17+83\times9\)
\(=\left(83+17\right)\times9\)
\(=100\times9\)
\(=900\)
\(4\frac{1}{7}+7+8\frac{6}{7}\)
\(=\left(4\frac{1}{7}+8\frac{6}{7}\right)+7\)
\(=\left(8+4\right)+\left(\frac{1}{7}+\frac{6}{7}\right)+7\)
\(=12+\frac{7}{7}+7\)
\(=12+1+7\)
\(=20\)
~ Ủng hộ nhé
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{1}{16}< \dfrac{7}{16}< \dfrac{1}{2}< \dfrac{9}{16}< \dfrac{3}{4}< \dfrac{7}{8}< \dfrac{11}{9}< \dfrac{16}{9}< \dfrac{8}{3}< \dfrac{17}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) = 17/19 - 17/19 + 27/35 + 35/35 = 0 + 62/35
b) = 1/3 x 4/5 + 1/3 x6/5 + 1/3 x 2 = 1/3(4/5 + 6/5 + 2) = 1/3 x 4 = = 4/3
c) 4/7 x 2/9 + 4/7 x 7/9 + 2/3 = 4/7 x (2/9 + 7/9) + 2/3 = 4/7 x 1 + 2/3 = 26/21
A) 17/19 - 17/19 + 27/35 + 35/35 = 0 + 62/35
B) 1/3 x 4/5 + 1/3 x 6/5 + 1/3 x 2 = 1/3 x(4/5 + 6/5 x 2 ) = 1/3 x 4 = 4/3
c) TƯƠNG TỰ CÂU A VÀ B
* HOKTOT*
NHA
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(2-3+5-7+9-11+13-15+17=\left(2+5+9+13+17\right)-\left(3+7+11+15\right)\)
\(=46-36=10\)
b)\(\frac{1}{1.2}+\frac{1}{2.3}+...............+\frac{1}{8.9}=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.................+\frac{1}{8}-\frac{1}{9}\)
\(=\frac{1}{1}-\frac{1}{9}=\frac{9}{9}-\frac{1}{9}=\frac{8}{9}\)
Áp dụng \(\frac{1}{n.\left(n+1\right)}=\frac{1}{n}-\frac{1}{n+1}\)
Chúc bạn học tốt
Đề là tính bằng cách hợp lý đúng ko bạn
a, 2-3+5-7+9-11+13-15+17
= (5+13) - (3+15) + (2+9-11) + (17-7)
= 18 - 18 + 0 +10
= 10
b, \(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)
\(=1-\frac{1}{9}\)
\(=\frac{8}{9}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
8/3 + 17/9 + 19/13 + 1/3 + 7/13 + 1/9 = ( 8/3 + 1/3 ) + (17/9 + 1/9 ) + (19/13 + 7/13)
= 3 + 2 + 2
=7
tích cho mk nha , !!!
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\(\dfrac{5}{6}\) + \(\dfrac{7}{8}\)
= \(\dfrac{5\times4}{6\times4}\) + \(\dfrac{7\times3}{8\times3}\)
= \(\dfrac{20}{24}\) + \(\dfrac{21}{24}\)
= \(\dfrac{41}{24}\)
5/6 + 7/8 = 41/24
2 + 2/3 = 8/3
7/9 - 1/7 = 40/63
1-1/11 =10/11
2x17/81 = 34/81
9/11 : 5/6 = 54/55
3: 12/25 = 25/4
Tick cho mik nhé.
Chúc bạn học tốt nha !