Question

Answer 1

\(\dfrac{7}{9}=\dfrac{77}{99}=\dfrac{777}{999}\)

\(\Rightarrow\dfrac{7}{9}=\dfrac{7\times11}{9\times11}=\dfrac{7\times111}{9\times111}\)

\(\Rightarrow\dfrac{7}{9}=\dfrac{7}{9}=\dfrac{7}{9}\)

b)\(\dfrac{39+13}{84+52}=\dfrac{78+26}{168+104}\)

Ta có:​​​\(\dfrac{78+26}{168+104}=\dfrac{2\times39+2\times13}{2\times84+2\times52}\)\(=\dfrac{2\times\left(39+13\right)}{2\times\left(84+52\right)}\)​

\(\Rightarrow\dfrac{39+13}{84+52}=\dfrac{2\left(39+13\right)}{2\left(84+52\right)}\)

\(\Rightarrow\dfrac{39+13}{84+52}=\dfrac{39+13}{84+52}\)

Vậy.......

c)vào giải luôn nhé

\(\dfrac{11\times12\times13+2\times11\times2\times12\times2\times13+3\times11\times3\times12\times3\times13}{12\times13\times14+2\times12\times2\times13\times2\times14+3\times12\times3\times13\times3\times14}\)

\(\dfrac{11\times12\times13+8\times\left(11\times12\times13\right)+27\times\left(11\times12\times13\right)}{12\times13\times14+2\times\left(12\times13\times14\right)+27\times\left(12\times13\times14\right)}\)

\(\dfrac{11\times12\times13\left(1+8+27\right)}{12\times13\times14\left(1+8+27\right)}\)

\(\Rightarrow\dfrac{11}{14}\)

đề này sai

 

Answer 2

Bài 5: 

a) \(\dfrac{77}{99}=\dfrac{77:11}{99:11}=\dfrac{7}{9}\)

\(\dfrac{777}{999}=\dfrac{777:111}{999:111}=\dfrac{7}{9}\)

Do đó: \(\dfrac{7}{9}=\dfrac{77}{99}=\dfrac{777}{999}\)

b) \(\dfrac{39+13}{84+52}=\dfrac{52}{136}=\dfrac{13}{34}\)

\(\dfrac{78+26}{168+104}=\dfrac{104}{272}=\dfrac{13}{34}\)

Do đó: \(\dfrac{39+13}{84+52}=\dfrac{78+26}{168+204}\)