\(B7:\\ a,\dfrac{5}{21}+0,5-\dfrac{19}{23}+\dfrac{16}{21}-\dfrac{4}{23}.\\ =\left(\dfrac{5}{21}+\dfrac{16}{21}\right)-\left(\dfrac{19}{23}+\dfrac{4}{23}\right)+0,5.\\ =1-1+0,5=0,5.\)
\(B8:\\ a,\left(\dfrac{3}{4}+\dfrac{2}{3}\right):\dfrac{17}{4}-\dfrac{3}{4}.\\ =\dfrac{17}{12}:\dfrac{17}{4}-\dfrac{3}{4}.\\ =\dfrac{1}{3}-\dfrac{3}{4}=-\dfrac{5}{12}.\\ b,\left(-5\right)^2.\dfrac{7}{45}+\left(-5\right)^2.\dfrac{11}{45}.\\ =\left(-5\right)^2\left(\dfrac{7}{45}+\dfrac{11}{45}\right).\\ =25.\dfrac{2}{5}=10.\)
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