\(\dfrac{12}{13}\)= \(\dfrac{12.101}{13.101}\)= \(\dfrac{1212}{1313}\) (1)
\(\dfrac{12}{13}\) = \(\dfrac{12.\left(-10101\right)}{13.\left(-10101\right)}\) = \(\dfrac{-121212}{-131313}\)(2)
Từ (1) và (2) => \(\dfrac{12}{13}=\dfrac{1212}{1313}=\dfrac{-121212}{-131313}\)