Bài 161 (Sách giáo khoa trang 64)

Gửi bởi: Sách Giáo Khoa Vào 26 tháng 12 2018 lúc 11:14:40

Tìm giá trị của biểu thức :

\(A=-1,6:\left(1+\dfrac{2}{3}\right)\)

\(B=1,4.\dfrac{15}{49}-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):2\dfrac{1}{5}\)

\(A=-1,6:\left(1+\dfrac{2}{3}\right)\)

\(\Rightarrow A=\dfrac{-8}{5}:\left(1+\dfrac{2}{3}\right)\)

\(\Rightarrow A=\dfrac{-8}{5}:\left(\dfrac{3}{3}+\dfrac{2}{3}\right)\)

\(\Rightarrow A=\dfrac{-8}{5}:\dfrac{5}{3}\)

\(\Rightarrow A=\dfrac{-8}{5}.\dfrac{3}{5}\)

\(\Rightarrow A=\dfrac{-24}{25}\)

\(B=1,4.\dfrac{15}{49}-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):2\dfrac{1}{5}\)

\(\Rightarrow B=\dfrac{7}{5}.\dfrac{15}{49}-\left(\dfrac{12}{15}+\dfrac{10}{15}\right):\dfrac{11}{5}\)

\(\Rightarrow B=\dfrac{3}{7}-\dfrac{22}{15}.\dfrac{5}{11}\)

\(\Rightarrow B=\dfrac{3}{7}-\dfrac{2}{3}\)

\(\Rightarrow B=\dfrac{9}{21}-\dfrac{14}{21}\)

\(\Rightarrow B=\dfrac{9}{21}+\left(\dfrac{-14}{21}\right)\)

\(\Rightarrow B=\dfrac{-5}{21}\)