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\(A=\dfrac{-5}{7}.\dfrac{2}{11}+\dfrac{-5}{7}.\dfrac{9}{11}+1\dfrac{5}{7}\)
\(=\dfrac{-5}{7}\left(\dfrac{2}{11}+\dfrac{9}{11}\right)+1+\dfrac{-5}{7}\)
\(=\dfrac{-5}{7}+\dfrac{-5}{7}+1=\dfrac{-3}{7}\)
\(B=0,7.2\dfrac{2}{3}.20.0,375.\dfrac{5}{28}\)
\(=\dfrac{7}{10}.\dfrac{8}{3}.20.\dfrac{3}{8}.\dfrac{5}{28}\)
\(=\dfrac{7}{10}.\dfrac{5}{28}.20=\dfrac{5}{2}.\)
Ta có :
A = \(\dfrac{-5}{7}.\dfrac{2}{11}+\dfrac{-5}{7}.\dfrac{9}{11}+1\dfrac{5}{7}\)
= \(\dfrac{5}{7}.\dfrac{-2}{11}-\dfrac{5}{7}.\dfrac{9}{11}+\dfrac{5}{7}+1\)
= \(\left(\dfrac{5}{7}.\dfrac{-2}{11}-\dfrac{5}{7}.\dfrac{9}{11}+\dfrac{5}{7}\right)+1\)
= \(\dfrac{5}{7}.\left(\dfrac{-2}{11}-\dfrac{9}{11}+1\right)+1\)
= \(\dfrac{5}{7}.0+1\)
= 1
B = \(0,7.2\dfrac{2}{3}.20.0,375.\dfrac{5}{28}\)
= \(\dfrac{7}{10}.\dfrac{8}{3}.20.\dfrac{3}{8}.\dfrac{5}{28}\)
= \(\left(\dfrac{7}{10}.20\right).\left(\dfrac{8}{3}.\dfrac{3}{8}\right).\dfrac{5}{28}\)
= 14.1.\(\dfrac{5}{28}\)
= \(\dfrac{5}{2}\)
Vậy A = 1
B = \(\dfrac{5}{2}\)
\(4\dfrac{1}{3}.\dfrac{4}{9}+13\dfrac{2}{3}.\dfrac{4}{9}\)\(=\dfrac{4}{9}\left(4\dfrac{1}{3}+13\dfrac{2}{3}\right)=\dfrac{4}{9}.18=8\)
\(5\dfrac{1}{4}.\dfrac{3}{8}+10\dfrac{3}{4}.\dfrac{3}{8}=\dfrac{3}{8}\left(5\dfrac{1}{4}+10\dfrac{3}{4}\right)=\dfrac{3}{8}.16=6\)
3/ Chu vi hình chữ nhật:
\(\left(\dfrac{1}{4}+\dfrac{3}{10}\right)\cdot2=\dfrac{11}{10}\) (chưa biết đơn vị)
Diện tích hình chữ nhật:
\(\dfrac{1}{4}\cdot\dfrac{3}{10}=\dfrac{11}{20}\) (chưa biết đơn vị)
bạn cứ tính 2 vế là xong mà:
a) x\(\in\){1;2;3;4;5;6;7}
b) x=0
1,=0 . [2017/2018+2018/2019]
=>0
2,TH1 x-3=0=>x=3
TH2 y-4=0=>y=4
3, -2/4 = -x/10 = 16/y
=>-1/2 = -x/10 = 16/y
=>-1/2 = -x/10 => -5/10 = -x/10 => x=5
-1/2 = 16/y => 16/-32 = 16/y => y = -32
S=\(\dfrac{1}{1}-\dfrac{1}{4} +...+\dfrac{1}{94}-\dfrac{1}{97}+\dfrac{1}{97}-\dfrac{1}{100}\)
S=\(\dfrac{1}{1}-\dfrac{1}{100}\)
S=1-\(\dfrac{1}{100}\)
S=\(\dfrac{99}{100}\)
a) \(\left(\dfrac{-3}{4}+\dfrac{2}{5}\right):\dfrac{3}{7}+\left(\dfrac{3}{5}+\dfrac{-9}{4}\right):\dfrac{3}{7}\)
\(=\left(\dfrac{-3}{4}+\dfrac{2}{5}+\dfrac{3}{5}+\dfrac{-9}{4}\right):\dfrac{3}{7}\)
\(=-2:\dfrac{3}{7}=\dfrac{-14}{3}\)
\(\dfrac{7}{8}:\left(\dfrac{2}{9}-\dfrac{1}{18}\right)+\dfrac{7}{8}:\left(\dfrac{1}{36}-\dfrac{5}{12}\right)\)
\(=\dfrac{7}{8}:\dfrac{1}{6}+\dfrac{7}{8}:\dfrac{-7}{18}\)
\(=\dfrac{7}{8}:\left(\dfrac{1}{6}+\dfrac{-7}{18}\right)=\dfrac{7}{8}:\dfrac{-2}{9}=\dfrac{63}{-16}\)
còn phần b