\(a,\dfrac{4}{5}+0,5+\dfrac{1}{5}-1\dfrac{1}{2}\) \(=\dfrac{4}{5}+\dfrac{1}{2}+\dfrac{1}{5}-\dfrac{3}{2}\)
\(=\dfrac{4}{5}+\dfrac{1}{5}+\dfrac{1}{2}-\dfrac{3}{2}\)
\(=\dfrac{5}{5}-\dfrac{2}{2}\)
\(=1-1\)
\(=0\)
\(b,15\dfrac{2}{5}.\left(-\dfrac{5}{4}\right)-3\dfrac{2}{5}.\left(-\dfrac{5}{4}\right)\) \(=\dfrac{77}{5}.\left(-\dfrac{5}{4}\right)-\dfrac{17}{5}.\left(-\dfrac{5}{4}\right)\)
\(=\left(-\dfrac{5}{4}\right).\left(\dfrac{77}{5}-\dfrac{17}{5}\right)\)
\(=\left(-\dfrac{5}{4}\right).12\)
\(=-15\)
\(c,\dfrac{2}{3}+\dfrac{7}{21}-1\dfrac{1}{12}+\dfrac{1}{12}\) \(=\dfrac{2}{3}+\dfrac{1}{3}-\dfrac{13}{12}+\dfrac{1}{12}\)
\(=\dfrac{3}{3}-\dfrac{12}{12}\)
\(=1-1\)
\(=0\)
\(d,\left(2-\dfrac{5}{2}\right)^2:\dfrac{1}{4}+\dfrac{3}{4}.\dfrac{-8}{6}\) \(=\left(-\dfrac{1}{2}\right)^2.4-1\)
\(=\dfrac{1}{4}.4-1\)
\(=1-1=0\)
\(e,36.\left(-\dfrac{1}{6}\right)^2+\dfrac{6}{7}\)\(=36.\dfrac{1}{36}+\dfrac{6}{7}\)
\(=1+\dfrac{6}{7}\)
\(=\dfrac{13}{7}\)
