Question

Bài 2. Tìm x, biết:

1) \(\dfrac{3}{x-1}\) = \(\dfrac{21}{16}\)             2) ( \(\dfrac{1}{3}\) - \(\dfrac{3}{2}\) x )² = 2\(\dfrac{1}{4}\)

3) \(\dfrac{1}{3}\) : x + 0,5 = \(\dfrac{17}{6}\)      4) 2,5x - 1 = 1,7x - \(\dfrac{3}{8}\)

Answer 1

\(1\text{)}\dfrac{3}{x-1}=\dfrac{21}{16}\Leftrightarrow3\cdot16=21\cdot\left(x-1\right)\)

=> 48 = 21 × (x - 1) => x - 1 = 48/21 => x = 23/7

2) 

\(\left(\dfrac{1}{3}-\dfrac{3}{2}x\right)^2=2\dfrac{1}{4}\Rightarrow\left(\dfrac{1}{3}-\dfrac{3}{2}x\right)^2=\dfrac{9}{4}\\ \Rightarrow\dfrac{1}{3}-\dfrac{3}{2}x=\dfrac{3}{2}\\ \Rightarrow\dfrac{3}{2}x=\dfrac{1}{3}-\dfrac{3}{2}=-\dfrac{7}{6}\\ \Rightarrow x=-\dfrac{7}{6}:\dfrac{3}{2}=-\dfrac{7}{9}\)

3)

\(\dfrac{1}{3}:x+0,5=\dfrac{17}{6}\\ \dfrac{1}{3}:x=\dfrac{7}{3}\\ x=\dfrac{1}{3}:\dfrac{7}{3}=\dfrac{1}{7}\)

4)

\(2,5x-1=1,7x-\dfrac{3}{8}\\ 2,5x-1,7x=1-\dfrac{3}{8}\\ 0,8x=\dfrac{5}{8}\\ x=\dfrac{25}{32}\)