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Bài 1:
BCNN(120,15,38)
Ta có: 120 = 23 . 3 . 5
15 = 3 . 5
38 = 2 . 19
~> BCNN(120,15,38) = 23 . 3 . 5 . 19 = 2280
BCNN(27,39,63)
Ta có: 27 = 33
39 = 3 . 13
63 = 32 . 7
~> BCNN(27,39,63) = 33 . 13 . 7 = 2457
=>x(x^2-9/16)=0
=>x(x-3/4)(x+3/4)=0
=>x=0; x=3/4; x=-3/4
\(\left(7\dfrac{4}{9}+4\dfrac{7}{11}\right)-3\dfrac{4}{9}\)
\(=\dfrac{67}{9}+\dfrac{51}{11}-\dfrac{31}{9}\)
\(=\dfrac{67}{9}-\dfrac{31}{9}+\dfrac{51}{11}\)
\(=4+\dfrac{51}{11}\)
\(=\dfrac{95}{11}\)
Chúc bạn học tốt
\(\frac{3}{5}+\frac{-1}{25}-\frac{7}{20}\)
\(=\frac{3}{5}-\frac{1}{25}-\frac{7}{20}\)
\(=\frac{60}{100}-\frac{4}{100}-\frac{35}{100}\)
\(=\frac{21}{100}\)
\(50\%x+\frac{2}{3}x=x-5\)
\(\Rightarrow\frac{1}{2}x+\frac{2}{3}x=x-5\)
\(\Rightarrow x\left(\frac{1}{2}+\frac{2}{3}\right)=x-5\)
\(\Rightarrow x.\frac{7}{6}=x-5\)
\(\Rightarrow x-\frac{7}{6}x=5\)
\(\Rightarrow\frac{-x}{6}=5\Leftrightarrow-x=30\Leftrightarrow x=-30\)
\(50\%x+\frac{2}{3}x=x-5\)
\(\frac{1}{2}x+\frac{2}{3}x=x-5\)
\(x\left(\frac{1}{2}+\frac{2}{3}\right)=x-5\)
\(x.\frac{7}{6}=x-5\)
\(x.\frac{7}{6}-x=-5\)
\(x.\frac{1}{6}=-5\)
\(x=\left(-5\right):\frac{1}{6}=-30\)
Vậy x= -30
\(\frac{x}{-4}=\frac{9}{-x}\)
\(\Leftrightarrow-x^2=-36\)
\(\Leftrightarrow x^2=36\)
\(\Leftrightarrow\orbr{\begin{cases}x=6\\x=-6\end{cases}}\)
Vậy............
\(\Leftrightarrow\frac{x}{-4}=\frac{-9}{x}\)
\(\Leftrightarrow x^2=36\)
\(\Rightarrow\orbr{\begin{cases}x=6\\x=-6\end{cases}}\)