a) \(\frac{\frac{2}{5}+\frac{2}{7}-\frac{2}{11}}{\frac{3}{5}+\frac{3}{7}-\frac{3}{11}}+\frac{\frac{1}{4}-\frac{1}{5}+\frac{1}{7}}{\frac{3}{4}-\frac{3}{5}+\frac{3}{7}}\)

\(=\frac{2\left(\frac{1}{5}+\frac{1}{7}-\frac{1}{11}\right)}{3\left(\frac{1}{5}+\frac{1}{7}-\frac{1}{11}\right)}+\frac{\frac{1}{4}-\frac{1}{5}+\frac{1}{7}}{3\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{7}\right)}\)

\(=\frac{2}{3}+\frac{1}{3}\)

\(=\frac{3}{3}\)

\(=1\)

1) tính:

a) 2.(1/5+1/7-1/11) / 3.(1/5+1/7-1/11) + 1.(1/4-1/5+1/7) / 3.(1/4-1/5+1/7)

=2/3+1/3=1

\(\frac{x}{4}-\frac{1}{y}=\frac{1}{2}\)

\(\Rightarrow\frac{1}{y}=\frac{x}{4}-\frac{1}{2}\)

\(\Rightarrow\frac{1}{y}=\frac{x-2}{4}\)

\(\Rightarrow\left(x-2\right)y=4\)

ta có bảng : 

vậy_

a, A= 9/6.(-1/12)=-1/8

b, B=-4+12.4/9+18.(-8/27)

=-4+16/3-16/3=-4

x=1; 2

\(\left(x-1\right)^3=\left(x-1\right)^2\)

\(\Rightarrow\left(x-1\right)^3-\left(x-1\right)^2=0\)

\(\Rightarrow\left(x-1\right)^2\left[\left(x-1\right)-1\right]=0\)

\(\Rightarrow\left(x-1\right)^2\cdot\left(x-2\right)=0\) 

\(\Rightarrow\orbr{\begin{cases}\left(x-1\right)^2=0\\x-2=0\end{cases}\Rightarrow\orbr{\begin{cases}x=1\\x=2\end{cases}}}\)

5x+1=+_6/7

+) 5x+1=6/7

x=-1/35

+) 5x+1=-6/7

x=-13/35

\(\frac{x}{5}=\frac{y}{7}=k\Rightarrow\hept{\begin{cases}x=5k\\y=7k\end{cases}}\)

\(x\cdot y=140\)

\(\Rightarrow5k\cdot7k=140\)

\(\Rightarrow35k^2=140\)

\(\Rightarrow k^2=4\)

\(\Rightarrow k=\pm2\)

\(k=2\Rightarrow\hept{\begin{cases}x=2\cdot5=10\\y=2\cdot7=14\end{cases}}\)

\(k=-2\Rightarrow\hept{\begin{cases}x=-2\cdot5=-10\\y=-2\cdot7=-14\end{cases}}\)

\(7x=3y\)

\(\Rightarrow\frac{x}{3}=\frac{y}{7}=k\Rightarrow\hept{\begin{cases}x=3k\\y=7k\end{cases}}\)

\(\Rightarrow x\cdot y=3k\cdot7k=2100\)

\(\Rightarrow21k^2=2100\)

\(\Rightarrow k^2=100\)

\(\Rightarrow k=\pm10\)

\(k=10\Rightarrow\hept{\begin{cases}x=10\cdot3=30\\y=10\cdot7=70\end{cases}}\)

\(k=-10\Rightarrow\hept{\begin{cases}x=-10\cdot3=-30\\y=-10\cdot7=-70\end{cases}}\)

4x=3y và 3x-y=21

a, 2x/6=3y/12=5z/25=>2x+3y+5z/ 6+12+25=86/43=2

=>x=2.3=6

y=2.4=8

z=2.5=10

\(a,\frac{x}{3}=\frac{y}{4}=\frac{z}{5}\)

\(\Rightarrow\frac{2y}{6}=\frac{3y}{12}=\frac{5z}{25}\)

\(\Rightarrow\frac{2x+3y+5z}{6+12+25}=\frac{x}{3}=\frac{y}{4}=\frac{z}{5}\) ma 2y + 3y + 5z = 86

\(\Rightarrow\frac{86}{43}=\frac{x}{3}=\frac{y}{4}=\frac{z}{5}\)

\(\Rightarrow2=\frac{x}{3}=\frac{y}{4}=\frac{z}{5}\)

\(\Rightarrow\hept{\begin{cases}x=2\cdot3=6\\y=2\cdot4=8\\z=2\cdot5=10\end{cases}}\)

x^2y-6x+3xy-18-(x^2y+2x-x-2)

x^2y-6x+3xy-18-x^2y-x+2

-7x+3xy-16