\(=\left(\dfrac{1}{6}+...+\dfrac{1}{9}\right)+\left(\dfrac{1}{10}+...+\dfrac{1}{19}\right)< \left(\dfrac{1}{4}+...+\dfrac{1}{4}\right)+\left(\dfrac{1}{10}+...+\dfrac{1}{10}\right)=2\)
4 số 10 số
\(B=\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+...+\dfrac{1}{18}+\dfrac{1}{19}\)
e) D = \(\dfrac{-5}{6}+\dfrac{-7}{12}-\dfrac{1}{3}\)
f) F = \(\dfrac{-3}{4}+\dfrac{1}{3}-\dfrac{-5}{18}\)
g) G = \(\dfrac{19}{9}-\dfrac{-4}{11}+\dfrac{2}{3}\)
h) H = \(\dfrac{5}{12}+\dfrac{-7}{4}-\dfrac{1}{-8}\)
Chứng minh:
\(\dfrac{1}{5}+\dfrac{1}{6}+\dfrac{1}{7}+...+\dfrac{1}{17}+\dfrac{1}{18}+\dfrac{1}{19}< 2\)
Bài 1.( 2 điểm)Tính bằng cách hợp lí:
a) \(\dfrac{1}{2}+\dfrac{9}{10}+\dfrac{5}{6}-\dfrac{11}{14}-\dfrac{1}{3}+\dfrac{-4}{35}\)
b) \(\left(\dfrac{18}{23}+\dfrac{7}{12}\right)+\left(\dfrac{-13}{19}-\dfrac{3}{4}\right)+\left(\dfrac{-6}{19}+\dfrac{5}{23}\right)\)
c) \(\dfrac{4}{3}+\dfrac{-5}{6}+\dfrac{-1}{4}\)
d) \(\dfrac{5}{6}-\dfrac{7}{5}+\dfrac{17}{30}\)
Tính bằng cách hợp lý:
\(a,\dfrac{2}{3}+\left(\dfrac{5}{7}+\dfrac{-2}{3}\right)\)
\(b,\left(\dfrac{-1}{4}+\dfrac{5}{8}\right)+\dfrac{-3}{8}\)
\(c,\dfrac{7}{5}.\dfrac{8}{19}+\dfrac{7}{5}.\dfrac{12}{19}-\dfrac{7}{5}.\dfrac{1}{19}\)
\(d,6\dfrac{3}{10}-\left(3\dfrac{4}{7}+2\dfrac{3}{10}\right)\)
\(e,\left(31,12-5,97\right)-\left(-68,88+4,03\right)\)
\(h,3,7.\left(-10,56\right)+3,7.110,56\)
*Thực hiện
1/ (\(\dfrac{2021}{2020}\)+\(\dfrac{2020}{2021}\)) x (\(\dfrac{1}{2}\)-\(\dfrac{1}{3}\)-\(\dfrac{1}{6}\))
2/ (\(\dfrac{7}{19}\)-\(\dfrac{5}{12}\)):\(\dfrac{-5}{8}\)-(\(\dfrac{7}{19}\)-\(\dfrac{29}{12}\)):\(\dfrac{5}{8}\)
3/ \(\dfrac{-5}{6}\)x\(\dfrac{7}{24}\)-\(\dfrac{5}{6}\)x\(\dfrac{14}{24}\)-\(\dfrac{5}{6}\)x\(\dfrac{3}{24}\)
Tính giá trị biểu thức
a, \(19\dfrac{5}{8}:\dfrac{7}{12}-15\dfrac{1}{4}:\dfrac{7}{12}\) b,\(\dfrac{2}{5}.\dfrac{1}{3}-\dfrac{2}{15}:\dfrac{1}{5}+\dfrac{3}{5}.\dfrac{1}{3}\)
c, \(\left(3\dfrac{1}{3}+2,5\right):\left(3\dfrac{1}{6}-4\dfrac{1}{5}\right)-\dfrac{11}{31}\) d, \(\left[6+\left(\dfrac{1}{2}\right)^3-\left|-\dfrac{1}{2}\right|\right]:\dfrac{3}{12}\)
1)\(\dfrac{1}{2}+\dfrac{13}{19}-\dfrac{4}{9}+\dfrac{6}{19}+\dfrac{5}{18}\)
2)\(\dfrac{ }{\dfrac{-20}{23}+\dfrac{2}{3}-\dfrac{3}{23}+\dfrac{2}{5}+\dfrac{7}{15}}\)
3)\(\dfrac{ }{\dfrac{4}{3}+\dfrac{-11}{31}+\dfrac{3}{10}-\dfrac{20}{31}-\dfrac{2}{5}}\)
4)\(\dfrac{ }{\dfrac{5}{7}.\dfrac{5}{11}+\dfrac{5}{7}.\dfrac{2}{11}-\dfrac{5}{7}.\dfrac{14}{11}}\)
a) A = \(\dfrac{19}{9}-\dfrac{-4}{11}-\dfrac{2}{-3}\)
b) B = \(\dfrac{-5}{6}+\dfrac{-7}{12}-\dfrac{1}{-5}\)
c) C = \(\dfrac{-3}{4}+\dfrac{11}{3}-\dfrac{-5}{18}\)
d) D = \(\dfrac{-19}{3}-\dfrac{4}{5}-\dfrac{-2}{3}\)
