a) -3/ 5:15 /18 b) -5 / 1:( -4) c)-28 : -7 / 25 d) 51/8 :-2/10
giúp mình nhanh nha ,cảm ơn
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\(A=\frac{\left[\left(25-1\right):1+1\right]\left(25+1\right)}{2}=325.\)
\(B=\frac{\left[\left(51-3\right):2+1\right]\left(51+3\right)}{2}=675\)
\(C=\frac{\left[\left(81-1\right):4+1\right]\left(81+1\right)}{2}=861\)
\(Y:\dfrac{7}{5}=\dfrac{5}{6}+\dfrac{5}{12}=\dfrac{15}{12}\\ Y=\dfrac{15}{12}\times\dfrac{7}{5}=\dfrac{7}{4}\)
\(y:\dfrac{7}{5}=\dfrac{5}{6}+\dfrac{5}{12}\\ \Leftrightarrow y:\dfrac{7}{5}=\dfrac{5\times2}{6\times2}+\dfrac{5}{12}\\ \Leftrightarrow y:\dfrac{7}{5}=\dfrac{10}{12}+\dfrac{5}{12}\\ \Leftrightarrow y:\dfrac{7}{5}=\dfrac{15}{12}\\ \Leftrightarrow y:\dfrac{7}{5}=\dfrac{5}{4}\\ \Leftrightarrow y=\dfrac{5}{4}\times\dfrac{7}{5}\\ \Leftrightarrow y=\dfrac{7}{4}\)
\(\Rightarrow C\)
\(a,\dfrac{-3}{5}:\dfrac{15}{18}=\dfrac{-3}{5}\times\dfrac{18}{15}=\dfrac{-3}{5}\times\dfrac{6}{5}=\dfrac{-18}{25}\\ b,\dfrac{-5}{1}:\left(-4\right)=\left(-5\right):\left(-4\right)=\dfrac{5}{4}\\ c,-28:\dfrac{-7}{25}=-28\times\dfrac{25}{-7}=100\\ d,\dfrac{51}{8}:\dfrac{-2}{10}=\dfrac{51}{8}\times\dfrac{10}{-2}=\dfrac{51}{8}\times\left(-5\right)=\dfrac{-255}{8}\)
\(a)-3/5*18/15=-18/25\)
\(b)-5*1/-4=5/4\)
\(c)-28*25/-7=-100\)
\(d)51/8*10/-2=-255/8\)