Quy đồng mẫu các phân số; a) $\frac{7}{30}$ ,$\frac{9}{-10}$ ,$\frac{-3}{25}$ b) $\frac{13}{60}$ ,$\frac{-7}{18}$ ,$\frac{-32}{90}$

Đáp án+Giải thích các bước giải:

 a) $\dfrac{7}{30}$, $\dfrac{9}{-10}$, $\dfrac{-3}{25}$       MSC: 150

$\dfrac{7}{30}$ = $\dfrac{7 .5}{30 .5}$ = $\dfrac{35}{150}$

$\dfrac{9}{-10}$ = $\dfrac{-9 .15}{10 .15}$ = $\dfrac{-135}{130}$

$\dfrac{-3}{25}$ = $\dfrac{-3 .6}{25 .6}$ = $\dfrac{-18}{150}$

Vậy quy đồng ba mẫu số đã cho ta được:

$\dfrac{7}{30}$ = $\dfrac{35}{150}$ ; $\dfrac{9}{-10}$ = $\dfrac{-135}{130}$ ; $\dfrac{-3}{25}$ = $\dfrac{-18}{25}$

b) $\dfrac{13}{60}$; $\dfrac{-7}{18}$; $\dfrac{-32}{90}$             MSC: 180

$\dfrac{13}{60}$ = $\dfrac{13 .3}{60 .3}$ = $\dfrac{39}{180}$

$\dfrac{-7}{18}$ = $\dfrac{-7 .10}{18 .10}$ = $\dfrac{-70}{180}$

$\dfrac{-32}{90}$ = $\dfrac{-32 .2}{90 .2}$ = $\dfrac{-64}{180}$

Vậy quy đồng ba mẫu số cho ta được:

$\dfrac{13}{60}$ = $\dfrac{39}{180}$ ; $\dfrac{-7}{18}$ = $\dfrac{-70}{180}$ ; $\dfrac{-32}{90}$ = $\dfrac{-64}{180}$