c)
\(15\times\left(-\dfrac{1}{5}\right)^2+\dfrac{1}{5}-2\times\left(-\dfrac{1}{2}\right)^3-\dfrac{1}{2}\)
\(=15\times\dfrac{1}{25}+\dfrac{1}{5}-2\times\dfrac{-1}{8}-\dfrac{1}{2}\)
\(=\dfrac{3}{5}+\dfrac{1}{5}-2\times\dfrac{-1}{8}-\dfrac{1}{2}\)
\(=\dfrac{3}{5}+\dfrac{1}{5}-\dfrac{-1}{4}-\dfrac{1}{2}\)
\(=\dfrac{4}{5}-\dfrac{-1}{4}-\dfrac{1}{2}\)
\(=\dfrac{16}{20}-\dfrac{-5}{20}-\dfrac{1}{2}\)
\(=\dfrac{21}{20}-\dfrac{1}{2}\)
\(=\dfrac{21}{20}-\dfrac{10}{20}\)
\(=\dfrac{11}{20}\)
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