Chọn mệnh đề đúng?
\(\dfrac{9}{70}< \dfrac{5}{42}.\)\(\dfrac{-4}{27}< \dfrac{10}{-63}\).\(\dfrac{-2}{15}>\dfrac{-10}{-11}.\)\(-0,6< \dfrac{-1}{2}.\)Hướng dẫn giải:+) \(\dfrac{9}{70}=\dfrac{27}{210};\dfrac{5}{42}=\dfrac{25}{210}\) mà \(\dfrac{27}{210}>\dfrac{25}{210}\Rightarrow\dfrac{9}{70}>\dfrac{5}{42}.\)
+) \(\dfrac{-4}{27}=\dfrac{-28}{189};\dfrac{10}{-63}=\dfrac{-30}{189}\) mà \(\dfrac{-28}{189}>\dfrac{-30}{189}\Rightarrow\dfrac{-4}{27}>\dfrac{10}{-63}.\)
+) \(\dfrac{-2}{15}< 0;\dfrac{-10}{-11}=\dfrac{10}{11}>0\Rightarrow\dfrac{-2}{15}< \dfrac{-10}{-11}.\)
+) \(\dfrac{-1}{2}=-0,5>-0,6.\)