Giá trị biểu thức \(A=\dfrac{-5}{6}.\dfrac{12}{-7}.\left(\dfrac{-21}{15}\right)\) là
\(2.\)\(-2.\)\(\dfrac{1}{2}.\)\(\dfrac{-1}{2}.\)Hướng dẫn giải:\(A=\dfrac{-5}{6}.\dfrac{12}{-7}.\left(\dfrac{-21}{15}\right)=\dfrac{\left(-5\right).12.\left(-21\right)}{6.\left(-7\right).15}=\dfrac{\left(-5\right).2.6.\left(-7\right).3}{6.\left(-7\right).5.3}=-2.\)
