\(A=\left(45\frac{1}{2}-2\frac{3}{8}\right)-\left(5\frac{5}{6}+6\frac{3}{4}\right)+\left(10\frac{2}{3}-5\frac{5}{8}\right)=?\)
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8 tháng 1 2020
1.
\(\frac{2x+3}{4}-\frac{5x+3}{6}=\frac{3-4x}{12}\)
\(MC:12\)
Quy đồng :
\(\Rightarrow\frac{3.\left(2x+3\right)}{12}-\left(\frac{2.\left(5x+3\right)}{12}\right)=\frac{3x-4}{12}\)
\(\frac{6x+9}{12}-\left(\frac{10x+6}{12}\right)=\frac{3x-4}{12}\)
\(\Leftrightarrow6x+9-\left(10x+6\right)=3x-4\)
\(\Leftrightarrow6x+9-3x=-4-9+16\)
\(\Leftrightarrow-7x=3\)
\(\Leftrightarrow x=\frac{-3}{7}\)
2.\(\frac{3.\left(2x+1\right)}{4}-1=\frac{15x-1}{10}\)
\(MC:20\)
Quy đồng :
\(\frac{15.\left(2x+1\right)}{20}-\frac{20}{20}=\frac{2.\left(15x-1\right)}{20}\)
\(\Leftrightarrow15\left(2x+1\right)-20=2\left(15x-1\right)\)
\(\Leftrightarrow30x+15-20=15x-2\)
\(\Leftrightarrow15x=3\)
\(\Leftrightarrow x=\frac{3}{15}=\frac{1}{5}\)
\(A=45+\frac{1}{2}-\left(2+\frac{3}{8}\right)-\left(5+\frac{5}{6}+6+\frac{3}{4}\right)+\left(10+\frac{2}{3}-5-\frac{5}{8}\right)\)
\(A=45+\frac{1}{2}-2-\frac{3}{8}-5-\frac{5}{6}-6-\frac{3}{4}+10+\frac{2}{3}-5-\frac{5}{8}\)
\(A=\left(45-2-5-6+10-5\right)+\left(\frac{1}{2}-\frac{3}{8}-\frac{5}{6}-\frac{3}{4}+\frac{2}{3}-\frac{5}{8}\right)\)
\(A=37+\left(\frac{1}{2}-\frac{3}{4}\right)+\left(-\frac{3}{8}-\frac{5}{8}\right)+\left(-\frac{5}{6}+\frac{2}{3}\right)=37-\frac{1}{4}-1-\frac{1}{6}\)
\(A=36-\frac{5}{12}=\frac{427}{12}\)