\(\cdot DuyNam\)
\(A=-\dfrac{7}{21}+\left(1+\dfrac{1}{3}\right)\)
\(A=-\dfrac{7}{21}+\dfrac{4}{3}\)
\(A=1\)
\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+-\dfrac{6}{9}\right)\)
\(B=\dfrac{2}{15}+-\dfrac{1}{9}\)
\(B=\dfrac{1}{45}\)
\(C=\left(-\dfrac{1}{5}+\dfrac{3}{12}\right)+-\dfrac{3}{4}\)
\(C=\dfrac{1}{20}+-\dfrac{3}{4}\)
\(C=-\dfrac{7}{10}\)