Bài 1.4 trang 7

Đề bài

So sánh các số hữu tỉ sau:

\(\begin{array}{l}a) - \dfrac{{57}}{{2021}}\,;\dfrac{1}{{6345}}\\b)\dfrac{{ - 19}}{{35}};\dfrac{{ - 13}}{{21}}\\c)\dfrac{6}{{73}};\dfrac{9}{{82}}\end{array}\)

Lời giải chi tiết

a)

\(\begin{array}{l} - \dfrac{{57}}{{2021}} < 0;\dfrac{1}{{6345}} > 0\\ \Rightarrow  - \dfrac{{57}}{{2021}} < \dfrac{1}{{6345}}\end{array}\)

b)

\( - \dfrac{{19}}{{35}} =- \dfrac{{19.3}}{{35.3}}=  - \dfrac{{57}}{{105}}; - \dfrac{{13}}{{21}} =- \dfrac{{13.5}}{{21.5}} =  -\dfrac{{65}}{{105}}\)

Mà -57 > -65 nên \( - \dfrac{{57}}{{105}} > -\dfrac{{ 65}}{{105}}\)

Nên \( - \dfrac{{19}}{{35}} >  - \dfrac{{13}}{{21}}\)

c)

\(\dfrac{6}{{73}} =\dfrac{6.3}{{73.3}} = \dfrac{{18}}{{219}};\dfrac{9}{{82}} = \dfrac{9.2}{{82.2}} = \dfrac{{18}}{{164}}\)

Mà 219 > 164 nên \(\dfrac{{18}}{{219}} < \dfrac{{18}}{{164}}\)

Nên \(\dfrac{6}{{73}} < \dfrac{9}{{82}}\)