\(a,\dfrac{3}{7}+\dfrac{2}{5}-\dfrac{3}{2}=\dfrac{30}{70}+\dfrac{28}{70}-\dfrac{105}{70}=\dfrac{-47}{70}\)
\(b,80:\left\{\left[21+\left(26-3^3\right)\right].2\right\}=80:\left\{\left[21+\left(26-27\right)\right].2\right\}=80:\left\{\left[21+\left(-1\right)\right].2\right\}=80:\left\{20.2\right\}=80:40=2\)
\(\dfrac{3}{7}+\dfrac{2}{5}-\dfrac{3}{2}\)
\(=\dfrac{15}{35}+\dfrac{14}{35}-\dfrac{3}{2}\)
\(=\dfrac{29}{35}-\dfrac{3}{2}\)
\(=\dfrac{58}{70}-\dfrac{105}{70}\)
\(=\dfrac{-47}{70}\)
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\(80:\left\{\left[21+\left(26-3\right)^3\right].2\right\}\)
\(=80:\left\{\left[21+23^3\right].2\right\}\)
\(=80:\left\{\left[21+12167\right].2\right\}\)
\(=80:\left\{12188.2\right\}\)
\(=80:24376\)
\(=\dfrac{10}{3047}\)
