Violympic toán 6
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Bài1. (4điểm) Thực hiện phép tính:
a) \(A=\dfrac{3}{5}+6\dfrac{5}{6}\left(11\dfrac{5}{20}-9\dfrac{1}{4}\right):8\dfrac{1}{3}\)
b) \(B=\dfrac{-1}{2}+\dfrac{-1}{6}+\dfrac{-1}{12}+\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)
tính a, \(\dfrac{5.4^{15}.9^9-4.30^{20}8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\)
b, 1\(\dfrac{1}{30}\):\(\left(24\dfrac{1}{6}-24\dfrac{1}{5}\right)-\dfrac{1\dfrac{1}{2}-\dfrac{3}{4}}{4x-\dfrac{1}{2}}=\left(-1\dfrac{1}{15}\right):\left(8\dfrac{1}{5}-8\dfrac{1}{3}\right)\)
23 tháng 2 2021 lúc 9:15
Tìm x :
a) \(\left|x+\dfrac{11}{17}\right|+\left|x+\dfrac{2}{17}\right|+\left|x+\dfrac{4}{17}\right|=4x\)
b) \(\left|x+\dfrac{1}{2}\right|+\left|x+\dfrac{1}{6}\right|+\left|x+\dfrac{1}{12}\right|+\left|x+\dfrac{1}{20}\right|+..+\left|x+\dfrac{1}{110}\right|=11x\)
Tìm x biết \(\left(\dfrac{1}{1.2.3.4}+\dfrac{1}{2.3.4.5}+\dfrac{1}{3.4.5.6}+...+\dfrac{1}{7.8.9.10}\right).x=\dfrac{119}{720}\)
chứng minh \(1^2+2^2+...+n^2=\dfrac{1}{3}n\left(n+\dfrac{1}{2}\right)\left(n+1\right)=\dfrac{1}{3}n^3+\dfrac{1}{2}n^2+\dfrac{1}{6}n\)
Tính:\(\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+...+\dfrac{1}{72}+\dfrac{1}{90}\)
27 tháng 3 2021 lúc 20:36
Tính:
\(E=\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\)
28 tháng 3 2021 lúc 10:19
Chứng minh rằng :
a) \(\dfrac{1.3.5.....39}{21.22.23.....40}=\dfrac{1}{2^{20}}\)
b) \(\dfrac{1.3.5....\left(2n-1\right)}{\left(n+1\right)\left(n+2\right)\left(n+3\right)...2n}=\dfrac{1}{2^n}\) với \(n\in\) N*
tìm x biết :
1.\(\dfrac{-5}{6}+\dfrac{8}{3}+\dfrac{-29}{6}\le x\le\dfrac{-1}{2}+2+\dfrac{5}{2}\)
2.\(\left(2,7x-1\dfrac{1}{2}x\right):\dfrac{2}{7}=\dfrac{-21}{4}\)
3.\(\left|2x-\dfrac{3}{4}\right|=1\)
làm hộ mik 3 con này cái