\(\dfrac{1}{17}-\dfrac{1}{17}.\dfrac{7}{2}=\dfrac{1}{17}-\dfrac{7}{34}=\dfrac{2}{34}-\dfrac{7}{34}=\dfrac{-5}{34}\)
\(\left(\dfrac{7}{5}+\dfrac{-2}{5}\right).\left(\dfrac{5}{7}+\dfrac{8}{21}\right)=1.\left(\dfrac{15}{21}+\dfrac{8}{21}\right)=1.\dfrac{23}{21}=\dfrac{23}{21}\)
\(\left[\dfrac{1}{3}-\left(\dfrac{1}{4}+\dfrac{-1}{2}\right)\right].\dfrac{2}{5}=\left[\dfrac{1}{3}-\dfrac{-1}{4}\right].\dfrac{2}{5}=\left[\dfrac{1}{3}+\dfrac{1}{4}\right].\dfrac{2}{5}=\dfrac{7}{12}.\dfrac{2}{5}=\dfrac{7}{30}\)
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