Question

Answer 1

Bài 5: 

a: 1/2-1/3=3/6-2/6=1/6

\(\dfrac{1}{2\cdot3}=\dfrac{1}{6}\)

Do đó: 1/2-1/3=1/2x3

b: \(\dfrac{1}{2\cdot3}=\dfrac{1}{6}=\dfrac{2}{12}\)

\(\dfrac{1}{3}-\dfrac{1}{5}=\dfrac{2}{15}\)

mà 2/12>2/15

nên \(\dfrac{1}{2\cdot3}>\dfrac{1}{3}-\dfrac{1}{5}\)

Answer 2

Bài 4:
\(\dfrac{3}{4}+\dfrac{2}{5}+\dfrac{3}{12}=\dfrac{3}{4}+\dfrac{2}{5}+\dfrac{1}{4}=\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\dfrac{2}{5}=1+\dfrac{2}{5}=\dfrac{7}{5}\\ \dfrac{47}{15}+\dfrac{40}{17}-\dfrac{4}{30}-\dfrac{6}{17}=\left(\dfrac{47}{15}-\dfrac{2}{15}\right)+\left(\dfrac{40}{17}-\dfrac{6}{17}\right)=3+2=5\)

Bài 5:
a,\(\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{3}{6}-\dfrac{2}{6}=\dfrac{1}{6}\)

\(\dfrac{1}{2\times3}=\dfrac{1}{6}\)

Vì \(\dfrac{1}{6}=\dfrac{1}{6}\Rightarrow\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{1}{2\times3}\)

b,\(\dfrac{1}{2\times3}=\dfrac{1}{6}=\dfrac{5}{30}\)

\(\dfrac{1}{3}-\dfrac{1}{5}=\dfrac{5}{15}-\dfrac{3}{15}=\dfrac{2}{15}=\dfrac{4}{30}\)

Vif \(\dfrac{5}{30}>\dfrac{4}{30}\Rightarrow\dfrac{1}{2\times3}>\dfrac{1}{3}-\dfrac{1}{5}\)