a.
Ta có: \(\dfrac{-3}{10}=\dfrac{-3.4}{10.4}=\dfrac{-12}{40}\)
Mà \(35\ne40\) nên \(\dfrac{-12}{35}\ne\dfrac{-12}{40}\) hay \(\dfrac{-12}{35}\ne\dfrac{-3}{10}\)
b.
\(\dfrac{-20}{45}=\dfrac{20}{-45}=\dfrac{5.4}{5.\left(-9\right)}=\dfrac{4}{-9}\)
Vậy \(\dfrac{4}{-9}=\dfrac{-20}{45}\)
\(a,\dfrac{-12}{35}=\dfrac{\left(-12\right).2}{35.2}=\dfrac{-24}{70};\dfrac{-3}{10}=\dfrac{-3.7}{10.7}=\dfrac{-21}{70}\\ Vì:\dfrac{-24}{70}\ne\dfrac{-21}{70}.Nên:\dfrac{-12}{35}\ne\dfrac{-3}{10}\\ ---\\ b,\dfrac{4}{-9}=\dfrac{4.\left(-5\right)}{\left(-9\right).\left(-5\right)}=\dfrac{-20}{45}\\ Vì:\dfrac{-20}{45}=\dfrac{-20}{45}.Nên:\dfrac{4}{-9}=\dfrac{-20}{45}\)
