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\(-\frac{7}{15}+\frac{5}{31}+\frac{-8}{15}+\frac{26}{31}=\frac{-7-8}{15}+\frac{5+26}{31}\)
\(=\frac{-15}{15}+\frac{31}{31}\)
\(=-1+1\)
= 0
\(\left(\frac{-7}{15}\right)+\frac{5}{31}+\left(\frac{-8}{15}\right)+\frac{26}{31}\)
\(=\left[\left(\frac{-7}{15}\right)+\left(\frac{-8}{15}\right)\right]+\left(\frac{5}{31}+\frac{26}{31}\right)\)
\(=\frac{-15}{15}+\frac{31}{31}\)
\(=-1+1\)
\(=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, 1 - 7x = 3x - 4
=> -7x - 3x = - 4 - 1
=> - 10x = - 5
=> x = 1/2
vậy_
b, đặt \(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{99}}\)
\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{98}}\)
\(3A-A=1-\frac{1}{3^{99}}\)
\(A=\frac{1-\frac{1}{3^{99}}}{2}\)
mk chỉ bt lm mấy phần hui à!
d)\(\frac{5}{17}+\frac{-4}{7}-\frac{20}{31}+\frac{12}{17}-\frac{11}{31}\)\(=\left(\frac{5}{17}+\frac{12}{17}\right)+\left(\frac{-20}{31}-\frac{11}{31}\right)+\frac{-4}{7}\)
\(=\frac{17}{17}+\frac{-31}{31}+\frac{-4}{7}\)\(=1+\left(-1\right)+\frac{-4}{7}\)\(=0+\frac{-4}{7}\)\(=-\frac{4}{7}\)
e)\(\frac{155-\frac{10}{7}-\frac{5}{11}+\frac{5}{23}}{403-\frac{20}{7}-\frac{13}{3}+\frac{13}{23}}\)
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Bài 1:
\(A=\frac{24.47-22}{24+47.23}.\frac{5+\frac{5}{7}+\frac{5}{11}-\frac{5}{13}+\frac{5}{1001}}{6+\frac{6}{7}+\frac{6}{11}-\frac{6}{13}+\frac{6}{1001}}\)\(=\frac{47.23+47-22}{24.47.23}.\frac{5\left(1+\frac{1}{7}+\frac{1}{11.}-\frac{1}{13}+\frac{1}{1001}\right)}{6\left(1+\frac{1}{7}+\frac{1}{11}-\frac{1}{13}+\frac{1}{1001}\right)}\)
\(=\frac{47.23+24}{24+47.23}.\frac{5}{6}\)
\(=1.\frac{5}{6}=\frac{5}{6}\)
Bài 2:
\(81^7-27^9-9^{13}=\left(3^4\right)^7-\left(3^3\right)^9-\left(3^2\right)^{13}\)
\(=3^{28}-3^{27}-3^{26}\)
\(=3^{22}\left(3^6-3^5-3^4\right)\)
\(=3^{22}.405\) chia hết cho 405
=>đpcm
\(-\frac{9}{22}+\frac{5}{31}+\frac{-13}{22}+\frac{88}{31}+\frac{1}{2}\)
\(=-1+3+\frac{1}{2}\)
\(=2+\frac{1}{2}\)
\(=\frac{5}{2}\)
= \(\left(\frac{-9}{22}+\frac{-13}{22}\right)+\left(\frac{5}{31}+2\frac{26}{31}\right)+0,5\)
= \(-1+3+0,5\)
= \(2+0,5\)
= \(2,5\)
k mik nhé
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