\(\dfrac{7}{9}:\dfrac{14}{15}-\dfrac{1}{2}=\dfrac{7}{9}x\dfrac{15}{14}-\dfrac{1}{2}=\dfrac{105}{126}-\dfrac{1}{2}=\dfrac{105}{126}-\dfrac{63}{126}=\dfrac{42}{126}=\dfrac{1}{3}\)

\(\dfrac{4}{5}+\dfrac{1}{10}=\dfrac{8}{10}+\dfrac{1}{10}=\dfrac{8+1}{10}=\dfrac{9}{10}\)

\(\dfrac{7}{12}-\dfrac{1}{4}=\dfrac{7}{12}-\dfrac{3}{12}=\dfrac{7-3}{12}=\dfrac{4}{12}=\dfrac{1}{3}\)

\(5\) x \(\dfrac{4}{15}=\)\(\dfrac{20}{15}=\dfrac{4}{3}\)

\(\dfrac{2}{5}:\dfrac{6}{5}=\dfrac{2}{5}\) x \(\dfrac{5}{6}=\dfrac{10}{30}=\dfrac{1}{3}\)

\(\dfrac{2}{5}\) x \(\dfrac{1}{4}:\dfrac{3}{2}=\dfrac{2}{20}:\dfrac{3}{2}=\dfrac{1}{10}:\dfrac{3}{2}=\dfrac{1}{10}\) x \(\dfrac{2}{3}=\dfrac{2}{30}\)
 

Đáp án : Tam giác cân.
 

\(\dfrac{7}{15}+\dfrac{1}{5}=\dfrac{7}{15}+\dfrac{3}{15}=\dfrac{7+3}{15}=\dfrac{10}{15}=\dfrac{2}{3}\)

               Bài giải

Đổi \(950km=95000000cm\)

Độ dài của quãng đường đó trên bản đồ là :

     \(95000000:1000000=95\left(cm\right)\)

          Đáp số : \(95cm.\)

\(\dfrac{49}{27}\) đã tối giản nên ta không rút gọn được.
 

a) \(\dfrac{3}{5}\) x \(\dfrac{17}{21}+\dfrac{17}{21}\) x \(\dfrac{2}{5}\)

\(=\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\) x \(\dfrac{17}{21}\)

\(=\dfrac{5}{5}\) x \(\dfrac{17}{21}\)

\(=1\) x \(\dfrac{17}{21}\)

\(=\dfrac{17}{21}\)

b) \(\dfrac{15}{8}:\dfrac{5}{20}-\dfrac{7}{8}:\dfrac{1}{4}\)

\(=\dfrac{15}{8}:\dfrac{1}{4}-\dfrac{7}{8}:\dfrac{1}{4}\)

\(=\left(\dfrac{15}{8}-\dfrac{7}{8}\right):\dfrac{1}{4}\)

\(=\dfrac{8}{8}:\dfrac{1}{4}\)

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

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

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

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

\(=4\)