\(\left(\dfrac{1}{5}+\dfrac{3}{10}\right):\left(2\dfrac{1}{3}\right)\\ =\left(\dfrac{2}{10}+\dfrac{3}{10}\right):\left(-\dfrac{7}{3}\right)\\ =\dfrac{5}{10}:\left(-\dfrac{7}{3}\right)\\ =\dfrac{1}{2}:\left(-\dfrac{7}{3}\right)\\ =\dfrac{1}{2}\cdot\left(-\dfrac{3}{7}\right)\\ =\dfrac{1\cdot\left(-3\right)}{2\cdot7}\\ =-\dfrac{3}{14}\)
tính nhanh
B = ( \(5\dfrac{9}{10}:\dfrac{3}{2}-\left(2\dfrac{1}{3}.4\dfrac{1}{2}-2.2\dfrac{1}{3}\right):\dfrac{7}{4}\)
Ai biết thì làm nhanh giúp mik nha
chieu nay mik đi hok rùi
BT2: Tính nhanh
5) \(1-\dfrac{1}{2}+2-\dfrac{2}{3}+3-\dfrac{3}{4}+4-\dfrac{1}{4}-3-\dfrac{1}{3}-2-\dfrac{1}{2}-1\)
6) \(\left(\dfrac{5}{7}-\dfrac{7}{5}\right)-\left[\dfrac{1}{2}-\left(-\dfrac{2}{7}-\dfrac{1}{10}\right)\right]\)
BT2: Tính nhanh
9) (\(\left(5+\dfrac{1}{5}-\dfrac{2}{9}\right)-\left(2-\dfrac{1}{23}-2\dfrac{3}{35}+\dfrac{5}{6}\right)-\left(8+\dfrac{2}{7}-\dfrac{1}{18}\right)\)
10)\(\dfrac{1}{3}-\dfrac{3}{4}-\left(-\dfrac{3}{5}\right)+\dfrac{1}{64}-\dfrac{2}{9}-\dfrac{1}{36}+\dfrac{1}{15}\)
Chứng minh rằng:
1) B =\(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}+...+\dfrac{1}{19}>1\)
2) \(A=\dfrac{1}{5}+\dfrac{2}{5^2}+\dfrac{3}{5^3}+\dfrac{4}{5^4}+...+\dfrac{500}{5^{500}}<100\)
3) \(C=\dfrac{1}{2^3}+\dfrac{1}{3^3}+\dfrac{1}{4^3}+\dfrac{1}{5^3}+...+\dfrac{1}{500^3}<\dfrac{1}{4}\)
4) \(D=\dfrac{4}{3}+\dfrac{10}{9}+\dfrac{28}{27}+...+\dfrac{3^{98}+1}{3^{98}}<100\)
Làm giúp mình sớm nha! Thanks.
tìm x
\([\dfrac{6:\dfrac{3}{5}-1\dfrac{1}{16}.\dfrac{16}{7}}{4\dfrac{1}{5}-\dfrac{10}{11}+5\dfrac{2}{11}}-\dfrac{\left(\dfrac{3}{20}+\dfrac{1}{2}-\dfrac{1}{5}\right).\dfrac{12}{49}}{3\dfrac{1}{3}+\dfrac{2}{9}}].x=2\dfrac{23}{96}\)
Bài 1: Tính nhanh:
a) \(\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{50}}\)
b)\(\dfrac{5}{3}+\dfrac{5}{3^2}+\dfrac{5}{3^3}+...+\dfrac{5}{3^{50}}\)
1 Tính:
a)\(\dfrac{\dfrac{7}{10}+\dfrac{3}{5}}{\dfrac{7}{10}+\dfrac{1}{2}}\) b)\(\dfrac{6-\dfrac{1}{\dfrac{1}{2}-\dfrac{1}{3}}}{6+\dfrac{1}{\dfrac{1}{2}-\dfrac{1}{3}}}\)
Bài 1:
a) \(\left[\dfrac{3}{20}-\dfrac{1}{5}x\right].1\dfrac{2}{3}=1\dfrac{1}{4}\)
b)\(\dfrac{-2}{3}.x+\dfrac{1}{5}=\dfrac{3}{10}\)
c)\(\dfrac{-2}{3} \)-\(\dfrac{1}{3}\left(2x-7\right)=\dfrac{3}{2}\)
1 thực hiện phép tính
a,\(\dfrac{-2}{3}+\dfrac{3}{4}-\dfrac{-1}{6}+\dfrac{-2}{6}-\dfrac{-2}{5}\)
b,\(\dfrac{-2}{3}+\dfrac{-1}{5}+\dfrac{3}{4}-\dfrac{5}{6}-\dfrac{-7}{10}\)
c,\(\dfrac{1}{2}-\dfrac{-2}{5}+\dfrac{1}{3}+\dfrac{5}{7}-\dfrac{-1}{6}+\dfrac{-4}{35}+\dfrac{1}{41}\)
d,\(\dfrac{1}{100.99}-\dfrac{1}{99.98}-\dfrac{1}{98.97}-...-\dfrac{1}{3.2}-\dfrac{1}{2.1}\)
