bai 14
C1
\(=3+\dfrac{1}{2}-\dfrac{2}{3}-2+\dfrac{2}{3}-\dfrac{5}{2}-5+\dfrac{5}{2}-\dfrac{4}{3}\)
\(=\left(3-2-5\right)+\left(\dfrac{1}{2}-\dfrac{5}{2}+\dfrac{5}{2}\right)+\left(\dfrac{-2}{3}+\dfrac{2}{3}-\dfrac{4}{3}\right)\)
\(=-4+\dfrac{1}{2}-\dfrac{4}{3}=-\dfrac{29}{6}\)
C2
\(=\dfrac{17}{6}-\dfrac{23}{6}-\dfrac{23}{6}=-\dfrac{29}{6}\)
bai 15
a/\(A=\dfrac{1}{3}-\dfrac{3}{4}+\dfrac{3}{5}+\dfrac{1}{72}-\dfrac{2}{9}-\dfrac{1}{36}+\dfrac{1}{15}\)
\(=\left(\dfrac{1}{3}-\dfrac{2}{9}\right)+\left(\dfrac{3}{5}+\dfrac{1}{15}\right)+\left(-\dfrac{3}{4}+\dfrac{1}{72}-\dfrac{1}{36}\right)\)
\(=\dfrac{1}{9}+\dfrac{2}{3}-\dfrac{55}{72}=-\dfrac{95}{72}\)
b/ \(B=\left(\dfrac{1}{5}-\dfrac{1}{5}\right)-\left(\dfrac{3}{7}-\dfrac{3}{7}\right)+\left(\dfrac{5}{9}-\dfrac{5}{9}\right)+\left(\dfrac{-1}{11}+\dfrac{2}{11}\right)+\left(\dfrac{7}{13}-\dfrac{7}{13}\right)-\dfrac{9}{16}\)
\(=0-0+0+\dfrac{1}{11}+0-\dfrac{9}{16}\)
\(=\dfrac{1}{11}-\dfrac{9}{16}=-\dfrac{83}{176}\)
