Question

Tìm x biết:

a) \(\frac{x-1}{3}=\frac{4}{2}\)

b) \(\left(\frac{3x}{7}+1\right):4=\frac{-1}{28}\)

c) \(\frac{2x}{4}=\frac{9}{2}\)

 

Answer 1

\(a\))  \(\frac{x-1}{3}=\frac{4}{2}=2\)

       \(x-1=2\times3=6\)

        \(x=6+1=7\)

b) \(\left(\frac{3x}{7}+1\right):4=-\frac{1}{28}\)

     \(\frac{3x}{7}+1=-\frac{1}{28}\times4=-\frac{1}{7}\)

      \(\frac{3x}{7}=-\frac{1}{7}-1=-\frac{8}{7}\)

\(3x=\left(-\frac{8}{7}\right)\times7=-8\)

\(x=-\frac{8}{3}\)

c) \(\frac{2x}{4}=\frac{9}{2}\)

\(2x=\frac{9}{2}\times4\)

\(2x=18\)

\(x=18:2=9\)

Answer 2

a, \(\frac{x-1}{3}=\frac{4}{2}=2\)

\(\Rightarrow x-1=2.3\)

\(x-1=6\)

\(x=6+1\)

\(x=7\)

Answer 3

a)  \(\Leftrightarrow2\left(x-1\right)=3\cdot4\)\(\Leftrightarrow2x-2=12\Leftrightarrow2x=12+2=14\)

\(\Leftrightarrow x=14:2\Leftrightarrow x=7\)

b)   \(\Leftrightarrow\frac{\frac{3x}{7}+1}{4}=\frac{-1}{28}\Leftrightarrow28\left(\frac{3x}{7}+1\right)=4\cdot-1\)

\(\Leftrightarrow\frac{28\cdot3x}{7}+28=-4\Leftrightarrow12x=-4-28=-32\)

\(x=-32:12=\frac{-8}{3}\)

c)  \(\Leftrightarrow2\cdot2x=4\cdot9\Leftrightarrow4x=36\Leftrightarrow x=36:4=9\)