Question

Bài 5: So sánh các số hữu tỉ sau:

a) -0,5 và \(\dfrac{-51}{100}\);                                       b) 1\(\dfrac{7}{9}\) và \(\dfrac{9}{5}\)

c) \(\dfrac{-295}{118}\) và \(\dfrac{-280}{133}\);                                  d) -\(\dfrac{15}{37}\) và \(\dfrac{10}{-29}\)

Answer 1

a) Ta có: \(\dfrac{-51}{100}=-0,51\)

Vì \(0,51>0,5\) nên \(-0,51< -0,5\)

hay \(-0,5>\dfrac{-51}{100}\)

b) Ta có: \(1\dfrac{7}{9}=\dfrac{16}{9}=\dfrac{80}{45}\); \(\dfrac{9}{5}=\dfrac{81}{45}\)

Vì \(80< 81\) nên \(\dfrac{80}{45}< \dfrac{81}{45}\)

hay \(1\dfrac{7}{9}< \dfrac{9}{5}\)

c) Có: \(\dfrac{-295}{118}-1=\dfrac{-295-118}{118}=\dfrac{-413}{118}\)

Lại có: \(\dfrac{-280}{133}-1=\dfrac{-280-133}{133}=\dfrac{-413}{133}\)

Vì \(118< 133\) nên \(\dfrac{1}{118}>\dfrac{1}{133}\)

\(\Rightarrow\dfrac{-413}{118}< \dfrac{-413}{133}\Rightarrow\dfrac{-295}{118}-1< \dfrac{-280}{133}-1\)

hay \(\dfrac{-295}{118}< \dfrac{-280}{133}\)

d) Ta có: \(-\dfrac{15}{37}< -\dfrac{15}{39}=-\dfrac{5}{13}=\dfrac{10}{-26}< \dfrac{10}{-29}\)

#$\mathtt{Toru}$