Nếu ?x12+9:7=3
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\(a,\dfrac{1}{2}-\dfrac{1}{3}-\left(-\dfrac{5}{4}\right)=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{5}{4}=\dfrac{1\times6-1\times4+5\times3}{12}=\dfrac{6-4+15}{12}=\dfrac{17}{12}\\ b,\dfrac{5}{4}-\dfrac{1}{2}-\dfrac{7}{8}=\dfrac{5\times2-1\times4-7}{8}=\dfrac{10-4-7}{8}=-\dfrac{1}{8}\\ c,\dfrac{1}{5}-\dfrac{1}{2}+\dfrac{9}{10}=\dfrac{1\times2-1\times5+9}{10}=\dfrac{2-5+9}{10}=\dfrac{6}{10}=\dfrac{3}{5}\\ d,\dfrac{5}{4}-\dfrac{1}{3}+\dfrac{7}{6}=\dfrac{5\times3-1\times4+7\times2}{12}=\dfrac{15-4+14}{12}=\dfrac{25}{12}\)
a/\(\dfrac{26}{15}+-\dfrac{7}{13}+-\dfrac{6}{13}-\dfrac{11}{15}\)
\(=\left(\dfrac{26}{15}-\dfrac{11}{15}\right)-\left(\dfrac{7}{13}+\dfrac{6}{13}\right)\)
\(=1-1\)
\(=0\)
b/Sửa đề:
\(-\dfrac{3}{4}\cdot\dfrac{4}{13}+-\dfrac{3}{4}\cdot\dfrac{9}{13}+\dfrac{3}{4}\)
\(=-\dfrac{3}{4}\cdot\left(\dfrac{4}{13}+\dfrac{9}{13}\right)+\dfrac{3}{4}\)
\(=-\dfrac{3}{4}\cdot1+\dfrac{3}{4}\)
\(=-\dfrac{3}{4}+\dfrac{3}{4}\)
\(=0\)
Câu 7:
\(2Al_2O_3\underrightarrow{^{đpnc}}4Al+3O_2\\ m_{Al_2O_3}=95\%.1=0,95\left(tấn\right)\\ m_{Al\left(LT\right)}=\dfrac{108.0,95}{204}=\dfrac{171}{340}\left(tấn\right)\\ Vì:H=98\%\\ \Rightarrow m_{Al\left(TT\right)}=\dfrac{171}{340}.98\%=\dfrac{8379}{17000}\left(tấn\right)=\dfrac{8379}{17}\left(kg\right)\)
\(\Leftrightarrow\left(10-x\right)\cdot2+7=\left(3+2\right)\cdot3=15\)
=>10-x=4
hay x=6
` 3/7 + 3/4 - 1/2 = 12/28 + 21/28 - 14/28 = 33/28 - 14/28 = 19/28`
` 6/11 + 2/9 xx 12 = 6/11 + 8/3 = 18/33 + 88/33 = 106/33`
` 5/7 - 8/5 : 4 = 5/7 - 8/5 xx 1/4 = 5/7 - 2/5 = 25/35- 14/35 = 11/35`
\(\dfrac{3}{7}+\dfrac{3}{4}-\dfrac{1}{2}=\dfrac{12}{28}+\dfrac{21}{28}=\dfrac{33}{28}-\dfrac{1}{2}=\dfrac{33}{28}-\dfrac{14}{28}=\dfrac{19}{28}\)
\(\dfrac{6}{11}+\dfrac{2}{9}\times12=\dfrac{54}{99}+\dfrac{22}{99}=\dfrac{76}{99}\times12=\dfrac{76\times12}{99}=\dfrac{912}{99}\)
\(\dfrac{5}{7}-\dfrac{8}{5}:4=\dfrac{5}{7}-\dfrac{8}{4}\times\dfrac{1}{4}=\dfrac{5}{7}-\dfrac{1}{2}=\dfrac{10}{14}-\dfrac{7}{14}=\dfrac{3}{14}\)
Cách 1:
A. \(\dfrac{17}{19}\) x \(\dfrac{12}{15}\) x \(\dfrac{19}{17}\)
= (\(\dfrac{17}{19}\) x \(\dfrac{19}{17}\)) x \(\dfrac{12}{15}\)
= \(1\) x \(\dfrac{12}{15}\)
= \(\dfrac{4}{5}\)
Cách hai:
A; \(\dfrac{17}{19}\) x \(\dfrac{12}{15}\) x \(\dfrac{19}{17}\)
= \(\dfrac{68}{95}\) x \(\dfrac{19}{17}\)
= \(\dfrac{4}{5}\)
bb vbvgcvbhu6ufxdbvv14564
? = (3-9/7)/12 = (12/7)/12=1/7