\(\dfrac{15}{19}.\dfrac{24}{23}.\dfrac{-19}{15}.\dfrac{23}{24}=-1\)
\(\dfrac{15}{19}.\dfrac{24}{23}.-\dfrac{19}{15}.\dfrac{23}{24}=\left(-\dfrac{19}{15}.\dfrac{15}{19}\right).\left(\dfrac{24}{23}.\dfrac{23}{24}\right)=-1.1=-1\)
\(\dfrac{15}{19}\cdot\dfrac{24}{23}\cdot\dfrac{-19}{15}\cdot\dfrac{23}{24}\)
\(=\dfrac{15}{19}\cdot\dfrac{-19}{15}\cdot\dfrac{23}{24}\cdot\dfrac{24}{23}\)
\(=-1\cdot1=-1\)