giúp tui đi

= 25 . 1/25.1/2 - 2 . 1/4 + 1/5

= 1. 1/2 - 2. 1/4  + 1/5

= 1/2- 2/4 +1/5

= 1/2- 1/2 +1/5

= 0+ 1/5

=1/5

giúp mình với đang cần gấp

Có \(\frac{x-1}{6}=\frac{x+5}{7}\)

\(\Leftrightarrow\frac{7\left(x-1\right)}{42}=\frac{6\left(x+5\right)}{42}\)

\(\Leftrightarrow7\left(x-1\right)=6\left(x+5\right)\)

\(\Leftrightarrow7x-7=6x+30\)

\(\Leftrightarrow7x-6x=7+30\)

\(\Leftrightarrow x=37\)

Vì \(\left|2x-4038\right|\ge0\)

\(\left(y-2020\right)^{2020}\ge0\)

\(\Rightarrow\left|2x-4038\right|+\left(y-2020\right)^{2020}\ge0\)

Mà \(\left|2x-4038\right|+\left(y-2020\right)^{2020}\le0\)

\(\Rightarrow\left|2x-4038\right|+\left(y-2020\right)^{2020}=0\)

\(\Rightarrow\orbr{\begin{cases}2x-4038=0\\y-2020=0\end{cases}\Rightarrow\orbr{\begin{cases}x=2019\\y=2020\end{cases}}}\)

3x-7/8=5/2

=>3x=20/8+7/8

=>3x=27/8

=>x=27/8:3

=>x=9/8

vậy x=9/8

x=9/8

2x=3y=5z

=> 2x/30=3y/30=5z/30

=> x/15=y/10=z/6

Áp dung tc dẫy tỉ số = nhau

=> x/15=y/10=z/6=x+y-z/15+10-6=95/19=5

=> x=5.15=75

      y=5.10=50

      z=5.6=30

vậy x=75;y=50;z=30

Vì \(\frac{x}{2}=\frac{y}{3}\Rightarrow\frac{x}{10}=\frac{y}{15}\)

    \(\frac{y}{5}=\frac{z}{7}\Rightarrow\frac{y}{15}=\frac{z}{21}\)

Aps dụng tích chất dãy tỉ số bằng nhau ta có

\(\frac{x}{10}=\frac{y}{15}=\frac{z}{21}=\frac{x+y+z}{10+15+21}=\frac{92}{46}=2\)

\(\Rightarrow x=10.2=20\)

\(y=15.2=30\)

\(z=21.2=42\)

Ta có 

\(\hept{\begin{cases}\frac{x}{2}=\frac{y}{3}\\\frac{y}{5}=\frac{z}{7}\end{cases}\Leftrightarrow\hept{\begin{cases}\frac{x}{10}=\frac{y}{15}\\\frac{y}{15}=\frac{z}{21}\end{cases}}\Leftrightarrow\frac{x}{10}=\frac{y}{15}=\frac{z}{21}}\)

Theo tính chất dãy tỉ số bằng nhau

\(\frac{x}{10}=\frac{y}{15}=\frac{z}{21}=\frac{x+y+z}{10+15+21}=\frac{92}{46}=2\)

Do đó \(\hept{\begin{cases}\frac{x}{10}=2\Rightarrow x=20\\\frac{y}{15}=2\Rightarrow y=30\\\frac{z}{21}=2\Rightarrow z=42\end{cases}}\)

Vậy x=20;y=30;z=42

Đặt \(x=2k;y=3k\) ta có

\(x.y=54\)

 \(2k.3k=54\)

\(6k^2=54\)

\(k^2=9\)

\(k=\pm3\)

\(\Rightarrow x=2.3=6\)                                                                \(\Rightarrow x=2.\left(-3\right)=-6\)  

\(y=3.3=-9\)                                                                \(y=3.\left(-3\right)=-9\)

ta có x/2=y/3

=>x.y/2.3=(x/2)^2

=>9=x^2/4

=> x^2=36

=> x=+- 6

=> y=+- 9

vậy x=+-6

      y=+-9