7/12

=4/12+3/12

=1/4+1/3

5/6

=3/6+2/6

=1/3+1/2

5/6=1/2+1/3

7/12=1/3+1/4

7/12=1/3+1/4

10/21=1/3+1/7

đúng ko

5/6=1/3+1/2

7/8=1/8+1/4+1/2

......................?

mik ko biết

mong bn thông cảm 

nha ................

7/12 = 1/3 + 1/4

5/6=1/6+2/3

\(\frac{1}{2}+\frac{1}{3}=\frac{5}{6}\)

\(\frac{1}{3}+\frac{1}{4}=\frac{7}{12}\)

Cho xin tk

\(\frac{5}{6}=\frac{1}{6}+\frac{4}{6}=\frac{1}{6}+\frac{2}{3}\) hoặc \(\frac{5}{6}=\frac{2}{6}+\frac{3}{6}=\frac{1}{3}+\frac{1}{2}\)

 \(\frac{7}{12}=\frac{1}{12}+\frac{6}{12}=\frac{1}{12}+\frac{1}{2}\) hoặc \(\frac{7}{12}=\frac{3}{12}+\frac{4}{12}=\frac{1}{4}+\frac{1}{3}\).......

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

\(\dfrac{13}{27}=\dfrac{9}{27}+\dfrac{4}{27}=\dfrac{1}{3}+\dfrac{4}{27}\)

\(\dfrac{7}{12}\) = \(\dfrac{1+6}{12}\) = \(\dfrac{1}{12}\) + \(\dfrac{6}{12}\) = \(\dfrac{1}{12}\) + \(\dfrac{1}{2}\)

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

\(\dfrac{13}{27}\) = \(\dfrac{1+12}{27}\) = \(\dfrac{1}{27}\) + \(\dfrac{12}{27}\) = \(\dfrac{1}{27}\) + \(\dfrac{4}{9}\)

\(\dfrac{13}{27}\) = \(\dfrac{4+9}{27}\) = \(\dfrac{4}{27}\) + \(\dfrac{9}{27}\) = \(\dfrac{4}{27}\) + \(\dfrac{1}{3}\)

\(\dfrac{13}{27}\) = \(\dfrac{6+7}{27}\) = \(\dfrac{6}{27}\) + \(\dfrac{7}{27}\) = \(\dfrac{2}{9}\) +  \(\dfrac{7}{27}\)

a, \(\dfrac{7}{12}=\dfrac{6+1}{12}=\dfrac{6}{12}+\dfrac{1}{12}=\dfrac{6}{6\times2}+\dfrac{1}{12}=\dfrac{1}{2}+\dfrac{1}{12}\)

b, \(\dfrac{13}{27}=\dfrac{12+1}{27}=\dfrac{12}{27}+\dfrac{1}{27}=\dfrac{3\times4}{3\times9}+\dfrac{1}{27}=\dfrac{4}{9}+\dfrac{1}{27}\)

đây là đáp án của mình ạ.