a) `1/x + 1/y = 7/12`

`=> (1.7)/(7x) + (1.7)/(7y) = (7.2)/(12.2)`

`=> 7/(7x) + 7/(7y) = 14/24`

`=> (7+7)/(7x) = (7+7)/(7y) = 14/24`

`=> 14/(7x) = 14/(7y) = 14/24`

`=> 7x=7y=24`

`=> x=y=24:7`

`=> x=y=24/7`

b) `1/x + 1/y = 5/6`

`=> (1.5)/(5x) + (1.5)/(5y) = (5.2)/(6.2)`

`=> 5/(5x) + 5/(5y) = 10/12`

`=> (5+5)/(5x) = (5+5)/(5y) = 10/12`

`=> 10/(5x) = 10/(5y) = 10/12`

`=> 5x=5y=12`

`=> x=y=12:5`

`=> x=y=12/5`

Đáp án:

`24/7`

`12/5`

Giải thích các bước giải:

$\Leftrightarrow$ $\dfrac{1}{x}$ `+` $\dfrac{1}{y}$ `= 7/12`

$\Leftrightarrow$ $\dfrac{1.7}{7x}$ `+` $\dfrac{1.7}{7y}$ `=` $\dfrac{7.2}{12.2}$

$\Leftrightarrow$ $\dfrac{7}{7x}$ `+` $\dfrac{7}{7y}$ `=` $\dfrac{14}{24}$

$\Leftrightarrow$ $\dfrac{7 + 7}{x}$ `=` $\dfrac{7 + 7}{y}$ `= 14/24`

$\Leftrightarrow$ $\dfrac{14}{7x}$ `=` $\dfrac{14}{y}$ `= 14/24`

$\Leftrightarrow$ `7x = 7y = 24`

$\Leftrightarrow$ `x = y = 24 :7`

$\Leftrightarrow$ `x = y = 24/7`

`1/x + 1/y =5/6`

$\Leftrightarrow$ `(1.5)/5x + (1.5)/5y = (5.2)/(6.2)`

$\Leftrightarrow$ `5/5x + 5/5y = 10/12`

$\Leftrightarrow$ `(5+5)/5x = (5 +5)/5y`

$\Leftrightarrow$ `10/5x = 10/5y = 10/12`

$\Leftrightarrow$ `5x = 5y =12`

$\Leftrightarrow$ `x = y = 12:5`

$\Leftrightarrow$ `x = y = 12/5`