a/ \(\dfrac{1}{3}+\dfrac{3}{4}-\dfrac{5}{6}\)               b/\(\dfrac{-2}{3}+\dfrac{6}{5}:\dfrac{2}{3}-\dfrac{2}{15}\)           c/\(\dfrac{-3}{7}+\dfrac{5}{13}+\dfrac{-4}{7}\)                    d/\(\dfrac{12}{19}+\dfrac{-8}{13}-\dfrac{12}{19}+\dfrac{5}{-13}+2\)

= \(\dfrac{4}{12}+\dfrac{9}{12}-\dfrac{10}{12}\)           = \(\dfrac{-2}{3}+\dfrac{9}{5}-\dfrac{2}{15}\)                 = \(\left(\dfrac{-3}{7}+\dfrac{-4}{7}\right)+\dfrac{5}{13}\)               =  \(\left[\dfrac{12}{19}+\left(-\dfrac{12}{9}\right)\right]+\left(\dfrac{-8}{13}+\dfrac{5}{-13}\right)+2\)

= \(\dfrac{13}{12}-\dfrac{10}{12}\)                    = \(\dfrac{-10}{15}+\dfrac{27}{15}-\dfrac{2}{15}\)              = \(\left(-1\right)+\dfrac{5}{13}\)                              =  \(0+\left(-1\right)+2\)

=  \(\dfrac{13-10}{12}\)                    = \(\dfrac{-17}{15}-\dfrac{2}{15}\dfrac{ }{ }\)                      = \(\dfrac{-13}{13}+\dfrac{5}{13}\)                              = \(\left(-1\right)+2\)

= \(\dfrac{2}{12}=\dfrac{1}{6}\)                     = \(\dfrac{\left(-17\right)-2}{15}\)                        = \(\dfrac{\left(-13\right)+5}{13}\)                               =  \(1\)

                                     = \(\dfrac{19}{15}\)                                     = \(\dfrac{-8}{13}\)