\(a,=-\dfrac{1}{8}-\dfrac{7}{8}+\dfrac{5}{24}+\dfrac{19}{24}=-1+1=0\\ b,=4+9-1=12\\ c,=\dfrac{4}{9}\cdot9-\dfrac{6}{7}\cdot\dfrac{1}{2}=4-\dfrac{3}{7}=\dfrac{25}{7}\)
\(a.\) \(\dfrac{-1}{8}+\dfrac{5}{24}-\dfrac{7}{8}+\dfrac{19}{24}\)
\(=\dfrac{1}{12}-\dfrac{7}{8}+\dfrac{19}{24}\)
\(=\dfrac{-19}{24}+\dfrac{19}{24}\)
\(=0\)
\(b.\sqrt{16}+\sqrt{81}-1^{2018}\)
\(=4+9-1\)
\(=12\)
\(c.\left(\dfrac{2}{3}\right)^2.9-\dfrac{6}{7}.\left|\dfrac{-1}{2}\right|\)
\(=\dfrac{4}{9}.9-\dfrac{6}{7}.\dfrac{1}{2}\)
\(=4-\dfrac{6}{7}.\dfrac{1}{2}\)
\(=4-\dfrac{3}{7}\)
\(=\dfrac{25}{7}\)
