a) \(\dfrac{5}{7}-x=-\dfrac{9}{21}\)
\(\Leftrightarrow x=\dfrac{5}{7}-\left(-\dfrac{9}{21}\right)\)
\(\Leftrightarrow x=\dfrac{15}{21}+\dfrac{9}{21}\)
\(\Leftrightarrow x=\dfrac{24}{21}=\dfrac{8}{7}\)
Vậy: \(x=\dfrac{8}{7}\)
b) \(-x-\dfrac{1}{9}=-\dfrac{2}{45}\)
\(\Leftrightarrow x+\dfrac{1}{9}=\dfrac{2}{45}\)
\(\Leftrightarrow x=\dfrac{2}{45}-\dfrac{1}{9}\)
\(\Leftrightarrow x=\dfrac{2}{45}-\dfrac{5}{45}\)
\(\Leftrightarrow x=-\dfrac{3}{45}=-\dfrac{1}{15}\)
Vậy: \(x=-\dfrac{1}{15}\)
c) \(\left|x+\dfrac{5}{6}\right|=\dfrac{11}{24}\)
\(\Leftrightarrow\left[{}\begin{matrix}x+\dfrac{5}{6}=\dfrac{11}{24}\\x+\dfrac{5}{6}=-\dfrac{11}{24}\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{11}{24}-\dfrac{5}{6}\\x=-\dfrac{11}{24}-\dfrac{5}{6}\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{11}{24}-\dfrac{20}{24}\\x=-\dfrac{11}{24}-\dfrac{20}{24}\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{9}{24}=-\dfrac{3}{8}\\x=-\dfrac{31}{24}\end{matrix}\right.\)
Vậy: \(x=-\dfrac{31}{24};-\dfrac{3}{8}\)
_Chúc bạn học tốt_
a, 5/7- x=-9/21=-3/7
x = 5/7 - (-3)/7
x=8/7
Vậy x=8/7 là giá trị cần tìm
biết 
bằng 6 lần tích các chữ số của nó.