Tính hợp lý
\(25\left(-\frac{1}{5}\right)^3+\frac{1}{5}-2\left(-\frac{1}{2}\right)^2-\frac{1}{2}\)
Nhanh nha
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17 tháng 9 2020
\(=\left(-\frac{1}{2}-\frac{1}{9}-\frac{7}{18}\right)+\left(\frac{3}{5}+\frac{2}{7}+\frac{4}{35}\right)+\frac{1}{127}\)
\(=\left(-\frac{9}{18}-\frac{2}{18}-\frac{7}{18}\right)+\left(\frac{21}{35}+\frac{10}{35}+\frac{4}{35}\right)+\frac{1}{127}\)
\(=\left(-\frac{18}{18}\right)+\frac{35}{35}+\frac{1}{127}\)
\(=-1+1+\frac{1}{127}\)
\(=\frac{1}{127}\)
26 tháng 9 2015
a) 0,4(3) = \(\frac{4,\left(3\right)}{10}=\frac{4+\frac{1}{3}}{10}=\frac{13}{30}\); 0,6(2) = \(\frac{6,\left(2\right)}{10}=\frac{6+\frac{2}{9}}{10}=\frac{56}{90}=\frac{28}{45}\); 0,5(8) = \(\frac{5,\left(8\right)}{10}=\frac{5+\frac{8}{9}}{10}=\frac{53}{90}\)
Vậy A = \(\frac{13}{30}+\frac{28}{45}.\frac{5}{2}-\frac{\frac{5}{6}}{\frac{53}{90}}:\frac{2700}{53}\) = \(\frac{13}{30}+\frac{14}{9}-\frac{5}{6}.\frac{90}{53}.\frac{53}{2700}=\frac{13}{30}+\frac{14}{9}-\frac{1}{36}=\frac{353}{180}\)
b) 0,(5) = 5/9; 0,(2) = 2/9
B = \(\left(\frac{5}{9}.\frac{2}{9}\right):\left(\frac{10}{3}.\frac{25}{33}\right)-\left(\frac{2}{5}.\frac{4}{3}\right):\frac{4}{3}\)
B = \(\frac{10}{81}.\frac{3.33}{10.25}-\frac{2}{5}=\frac{11}{225}-\frac{2}{5}=-\frac{79}{225}\)
4 tháng 7 2017
c) C = ( 1 - 2 ) + ( 3 - 4 ) + ... + ( 79 - 80 )
C = ( -1 ) + ( -1 ) + ... + ( -1 )
C = ( -1 ) x ( 80 - 1 + 1 ) : 2
C = ( -1 ) x 80 : 2
C = ( -40 )
chán thím ghê -,-
\(25\left(-\frac{1}{5}\right)^3+\frac{1}{5}-2\left(-\frac{1}{2}\right)^2-\frac{1}{2}\)
\(=\)\(\left(25.\frac{\left(-1\right)^3}{5^3}+\frac{1}{5}\right)-\left(2.\frac{\left(-1\right)^2}{2^2}+\frac{1}{2}\right)\)
\(=\)\(\left(25.\frac{-1}{5^3}+\frac{1}{5}\right)-\left(2.\frac{1}{2^2}+\frac{1}{2}\right)\)
\(=\)\(\frac{1}{5}\left(25.\frac{-1}{5^2}+1\right)-\frac{1}{2}\left(2.\frac{1}{2}+1\right)\)
\(=\)\(\frac{1}{5}\left(-1+1\right)-\frac{1}{2}\left(1+1\right)\)
\(=\)\(\frac{1}{5}.0-\frac{1}{2}.2\)
\(=\)\(-1\)