Tìm x, biết:
a)\( – x + \dfrac{7}{4} = \dfrac{6}{5} – \dfrac{3}{4}\)
b)\(1 – 2x = \dfrac{9}{8} + \dfrac{7}{5}:\dfrac{2}{5}\)
-Rút gọn vế phải
-Áp dụng quy tắc chuyển vế.
a)
\(\begin{array}{l} – x + \dfrac{7}{4} = \dfrac{6}{5} – \dfrac{3}{4}\\ \Rightarrow – x = \dfrac{6}{5} – \dfrac{3}{4} – \dfrac{7}{4}\\ \Rightarrow – x = \dfrac{24}{20} – \dfrac{{15}}{20}-\dfrac{{35}}{20}\\ \Rightarrow – x = \dfrac{{-26}}{{20}}\\ \Rightarrow x = \dfrac{{13}}{{10}}\end{array}\)
Vậy \(x=\dfrac{13}{10}\)
b)
\(\begin{array}{l}1 – 2x = \dfrac{9}{8} + \dfrac{7}{5}:\dfrac{2}{5}\\ \Rightarrow 1 – 2x = \dfrac{9}{8} + \dfrac{7}{5}.\dfrac{5}{2}\\\Rightarrow 1 – 2x = \dfrac{9}{8} + \dfrac{7}{2}\\ \Rightarrow 1 – 2x = \dfrac{{9 + 28}}{8}\\ \Rightarrow 2x = 1 – \dfrac{{37}}{8}\\ \Rightarrow 2x = \dfrac{{ – 29}}{8}\\ \Rightarrow x = – \dfrac{{29}}{8}:2\\ \Rightarrow x = – \dfrac{{29}}{8}.\dfrac{1}{2}\\ \Rightarrow x = – \dfrac{{29}}{{16}}\end{array}\)
Vậy \(x=\dfrac{-29}{16}\)