Bài 2:
1: \(A=\left(-2\dfrac{1}{5}+\dfrac{2}{7}-\dfrac{12}{13}\right)-\left(-\dfrac{5}{7}+\dfrac{1}{13}\right)\)
\(=-2-\dfrac{1}{5}+\dfrac{2}{7}-\dfrac{12}{13}+\dfrac{5}{7}-\dfrac{1}{13}\)
\(=-\dfrac{11}{5}+\left(\dfrac{2}{7}+\dfrac{5}{7}\right)+\left(-\dfrac{12}{13}-\dfrac{1}{13}\right)\)
\(=-\dfrac{11}{5}\)
2: Sửa đề: \(B=\dfrac{12}{17}\cdot\dfrac{5}{7}-\dfrac{-12}{17}\cdot\dfrac{1}{7}+12\cdot\dfrac{1}{17\cdot7}\)
\(=\dfrac{12}{17}\cdot\dfrac{5}{7}+\dfrac{12}{17}\cdot\dfrac{1}{7}+\dfrac{12}{17}\cdot\dfrac{1}{7}\)
\(=\dfrac{12}{17}\left(\dfrac{5}{7}+\dfrac{1}{7}+\dfrac{1}{7}\right)=\dfrac{12}{17}\)
3: \(C=\left(\dfrac{1}{3}-2\dfrac{1}{6}\right)^2:\left(-3\dfrac{13}{36}\right)\)
\(=\left(\dfrac{2}{6}-\dfrac{13}{6}\right)^2:\left(-3\dfrac{13}{36}\right)\)
\(=-\left(\dfrac{11}{6}\right)^2:\left(3+\dfrac{13}{36}\right)\)
\(=-\dfrac{121}{36}:\dfrac{121}{36}=-1\)
