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11 tháng 8 2017
a, \(\frac{4}{7}x\frac{5}{7}+\frac{3}{7}x\frac{5}{6}\)
= ( \(\frac{4}{7}+\frac{3}{7}\)) x \(\frac{5}{7}x\frac{5}{6}\)
= 1 x \(\frac{5}{7}x\frac{5}{6}\)
= \(\frac{5}{7}x\frac{5}{6}\)
= \(\frac{25}{42}\)
Tương tự mấy câu sau cũng làm như thế này
NA
3
14 tháng 7 2019
\(A=\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+...+\frac{1}{9.11}-\frac{1}{11.13}\)
\(\Leftrightarrow A=\frac{1}{1.3}-\frac{1}{11.13}=\frac{1}{3}-\frac{1}{143}=\frac{140}{429}\)
14 tháng 7 2019
\(A=\frac{4}{1.3.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+\frac{4}{7.9.11}+\frac{4}{9.11.13}\)
\(\Rightarrow A=\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+...+\frac{1}{9.11}-\frac{1}{11.13}\)
\(\Rightarrow A=\frac{1}{1.3}-\frac{1}{11.13}=\frac{1}{3}-\frac{1}{143}=\frac{140}{429}\)
H
1
H
18 tháng 7 2023
`!`
\(a,\dfrac{8}{9}\times\dfrac{7}{5}-\dfrac{7}{9}\times\dfrac{2}{5}+\dfrac{2}{9}\\ =\dfrac{8}{9}\times\left(\dfrac{7}{5}-\dfrac{2}{5}\right)+\dfrac{2}{9}\\ =\dfrac{8}{9}\times\dfrac{5}{5}+\dfrac{2}{9}\\ =\dfrac{8}{9}+\dfrac{2}{9}\\ =\dfrac{10}{9}\)
\(b,\dfrac{5}{9}\times\dfrac{1}{4}+\dfrac{4}{9}\times\dfrac{3}{12}\\ =\dfrac{5}{9}\times\dfrac{1}{4}+\dfrac{4}{9}\times\dfrac{1}{4}\\ =\dfrac{1}{4}\times\left(\dfrac{5}{9}+\dfrac{4}{9}\right)\\ =\dfrac{1}{4}\times\dfrac{9}{9}\\ =\dfrac{1}{4}\)
AK
1 tháng 6 2018
\(\frac{1}{3}+\frac{3}{7}+\frac{5}{3}+\frac{8}{14}\)
\(=\left(\frac{1}{3}+\frac{5}{3}\right)+\left(\frac{3}{7}+\frac{8}{14}\right)\)
\(=\frac{6}{3}+\left(\frac{6}{14}+\frac{8}{14}\right)\)
\(=2+\frac{14}{14}\)
\(=2+1\)
\(=3\)
\(\frac{5}{6}+\frac{4}{15}+\frac{6}{18}+\frac{3}{45}\)
\(=\left(\frac{5}{6}+\frac{6}{18}\right)+\left(\frac{4}{15}+\frac{3}{45}\right)\)
\(=\left(\frac{5}{6}+\frac{2}{6}\right)+\left(\frac{4}{15}+\frac{1}{15}\right)\)
\(=\frac{7}{6}+\frac{5}{15}\)
\(=\frac{7}{6}+\frac{1}{3}\)
\(=\frac{7}{6}+\frac{2}{6}\)
\(=\frac{9}{6}\)
\(=\frac{3}{2}\)
~ Ủng hộ nhé
AK
1 tháng 6 2018
\(9\times17+83\times9\)
\(=\left(83+17\right)\times9\)
\(=100\times9\)
\(=900\)
\(4\frac{1}{7}+7+8\frac{6}{7}\)
\(=\left(4\frac{1}{7}+8\frac{6}{7}\right)+7\)
\(=\left(8+4\right)+\left(\frac{1}{7}+\frac{6}{7}\right)+7\)
\(=12+\frac{7}{7}+7\)
\(=12+1+7\)
\(=20\)
~ Ủng hộ nhé
HN
3
TT
0
AM
14 tháng 6 2015
a)\(\frac{4}{3.7}+\frac{4}{7.11}+...+\frac{4}{23.27}=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{23}-\frac{1}{27}=\frac{1}{3}-\frac{1}{27}=\frac{8}{27}\)
b)\(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{6.7}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{6}-\frac{1}{7}=\frac{1}{2}-\frac{1}{7}=\frac{5}{14}\)
c)\(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{11.13}+\frac{2}{1.2}+\frac{2}{2.3}+...+\frac{2}{9.10}=\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{13}\right)+2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=\frac{1}{3}-\frac{1}{13}+2\left(1-\frac{1}{10}\right)=\frac{10}{39}+\frac{9}{5}=\frac{401}{195}\)
9 tháng 8 2015
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
4 tháng 3 2022
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
DD
25 tháng 9 2017
1.
\(a,\frac{1}{7}+\frac{3}{4}+\frac{2}{7}+\frac{4}{7}=\frac{1}{7}+\frac{2}{7}+\frac{4}{7}+\frac{3}{4}\)
\(=1+\frac{3}{4}=\frac{7}{4}.\)
\(b,\frac{4}{7}:\frac{2}{5}+\frac{3}{7}:\frac{2}{5}-\frac{7}{9}=\left(\frac{4}{7}+\frac{3}{7}\right):\frac{2}{5}-\frac{7}{9}\)
\(=1:\frac{2}{5}-\frac{7}{9}=\frac{5}{2}-\frac{7}{9}\)
\(=\frac{31}{18}.\)
25 tháng 9 2017
a)3/4+(1/7+2/7+4/7)
=3/4+1
=7/4
b)2/5:(4/7+3/7)-7/9
=2/5:1-7/9
=2/5-7/9
=-17/45
\(B=\frac{\frac{4}{3}+\frac{4}{5}-\frac{4}{9}}{\frac{7}{3}+\frac{7}{5}-\frac{7}{9}}\)
\(=\frac{4.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}{7.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}\)
\(=\frac{4}{7}\)
B= \(\frac{\frac{4}{3}+\frac{4}{5}-\frac{4}{9}}{\frac{7}{3}+\frac{7}{5}-\frac{7}{9}}\)=\(\frac{4.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}{7.\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{9}\right)}\)= \(\frac{4}{7}\)