X/42-30/42=-9/42
→x-30=-9
→x =-9+30
→x =21
\(\dfrac{x}{6}-\dfrac{5}{7}=\dfrac{-3}{14}\Leftrightarrow\dfrac{x}{6}=\dfrac{5}{7}-\dfrac{3}{14}=\dfrac{10-3}{14}=\dfrac{1}{2}\)
2x=6 => x=3
Doãn Đức Khiêm chuyện sai là bt
nhưng bạn làm quá tắt (đúng sai chưa cần biết)
\(\dfrac{x}{6}-\dfrac{5}{7}=-\dfrac{3}{14}\)
\(\dfrac{x}{6}=-\dfrac{3}{14}+\dfrac{5}{7}\)
\(\dfrac{x}{6}=-\dfrac{3}{14}+\dfrac{10}{14}\)
\(\dfrac{x}{6}=\dfrac{7}{14}=2\)
\(\Rightarrow\dfrac{x}{6}=2\)
\(\rightarrow x=2.6=12\)
