Question

1. Tìm x, biết;

a) \(\dfrac{4,5}{x}\) = \(\dfrac{3}{5}\)

b) \(\dfrac{-x}{\dfrac{4}{5}}\) = \(\dfrac{\dfrac{-1}{5}}{x}\)

c) \(\dfrac{x-3}{2}\) = \(\dfrac{x}{5}\)

Giúp mk vs

Answer 1

\(a,\dfrac{4,5}{x}=\dfrac{3}{5}\)

\(\Leftrightarrow3x=4,5.5\)

\(\Leftrightarrow3x=22,5\)

\(\Leftrightarrow x=7,5\)

Vậy ....

b, \(\dfrac{-x}{\dfrac{4}{5}}=\dfrac{\dfrac{-1}{5}}{x}\)

\(\Leftrightarrow\left(-x\right)x=\dfrac{4}{5}.\dfrac{-1}{5}\)

\(\Leftrightarrow\left(-x\right)x=\dfrac{-4}{25}\)

\(\Leftrightarrow\left(-x\right)x=\dfrac{-2}{5}.\dfrac{2}{5}\)

\(\Leftrightarrow x=\dfrac{2}{5}\)

Vậy ....

c, \(\dfrac{x-3}{2}=\dfrac{x}{5}\)

\(\Leftrightarrow\left(x-3\right)5=2x\)

\(\Leftrightarrow5x-15=2x\)

\(\Leftrightarrow5x-2x=15\)

\(\Leftrightarrow3x=15\)

\(\Leftrightarrow x=5\)

Vậy .......

Answer 2

Áp dụng công thức ra nhé :

\(\dfrac{4,5}{x}=\dfrac{3}{5}\Rightarrow3x=22,5\Rightarrow x=7,5\)

Câu b : Ko bt tính từ dưới lên hay từ trên xuống nữa

Câu cờ :

\(\dfrac{x-3}{2}=\dfrac{x}{5}\Rightarrow\left(x-3\right).5=2x\)

\(\Rightarrow5x-15-2x=0\)

\(\Rightarrow3x-15=0\)

\(\Rightarrow x=5\)