Bài 45 trang 26 SGK Toán 6 tập 2

Tìm x, biết:

a) \(x=\dfrac{-1}{2}+\dfrac{3}{4};\)                      b) \(\dfrac{x}{5}=\dfrac{5}{6}+\dfrac{-19}{30}\).

a) \(x=\dfrac{-1}{2}+\dfrac{3}{4};\)    

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

\(x= \dfrac{{ - 2}}{4} + \dfrac{3}{4} \)

\(x= \dfrac{{ - 2 + 3}}{4} \)

\(x= \dfrac{1}{4}\)

b) \(\dfrac{x}{5}=\dfrac{5}{6}+\dfrac{-19}{30}\)

\(\begin{array}{l}
\dfrac{x}{5} = \dfrac{5}{6} + \dfrac{{ - 19}}{{30}}\\
\dfrac{x}{5} = \dfrac{{25}}{{30}} + \dfrac{{ - 19}}{{30}}\\
\dfrac{x}{5} = \dfrac{6}{{30}} = \dfrac{1}{5}\\
x = 1
\end{array}\) 

ĐS. a) \(x=\dfrac{1}{4}\)                     b) \(x = 1.\)