Giúp em vs ạ em gấp lắm lun ý =>>
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M
20 tháng 7 2017
M=2/3.5+2/5.7+...+2/97.99
M=1/3-1/5+1/5-...+1/97-1/99
M=1/3-1/99
M=32/99
20 tháng 7 2017
\(M=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+....+\frac{2}{97.99}\)
\(=2\left(\frac{1}{3}+\frac{1}{5}-\frac{1}{5}+\frac{1}{7}-...-\frac{1}{97}+\frac{1}{99}\right)\)
\(=2\left(\frac{1}{3}-\frac{1}{99}\right)\)
\(=2.\frac{32}{99}\)
\(=\frac{64}{99}\)
gấp mn giúp em câu này vs ạ e gấp lắm mn giúp em vs em cảm ơn ạ
HN
1
HP
4 tháng 10 2021
a. PTHH: CuO + H2SO4 ---> CuSO4 + H2O
b. Ta có: \(n_{CuO}=\dfrac{8}{80}=0,1\left(mol\right)\)
Theo PT: \(n_{H_2SO_4}=n_{CuO}=0,1\left(mol\right)\)
=> \(m_{H_2SO_4}=0,1.98=9,8\left(g\right)\)
Ta có: \(C_{\%_{H_2SO_4}}=\dfrac{9,8}{m_{dd_{H_2SO_4}}}.100\%=4,9\%\)
=> \(m_{dd_{H_2SO_4}}=200\left(g\right)\)
c. Ta có: \(m_{dd_{CuSO_4}}=200+8=208\left(g\right)\)
Theo PT: \(n_{CuSO_4}=n_{CuO}=0,1\left(mol\right)\)
=> \(m_{CuSO_4}=0,1.160=16\left(g\right)\)
=> \(C_{\%_{CuSO_4}}=\dfrac{16}{208}.100\%=7,69\%\)
TT
3 tháng 7 2020
14. Wine used to be produced in this area
15. The Earth is said to be round
16. America is believed to have been discovered by Columbus
17. Five people are reported to have been injured in the accident
18. I will have the motorbike repaired by my brother
19. I remember being taken to the zoo by my father on Sundays
3 tháng 7 2020
14. Wine used to be produced in this area.
( S + used to + be + PII + by + O )
15. The Earth is said to be round.
16. America is believed to be discovered by Columbus.
17. Five people are reported to have been injured in the accident.
18. I will have the motorbike repaired by my brother.
19. I remember being taken to the zoo by my father on Sundays.
2 tháng 7 2021
Ta có: \(\sqrt{\dfrac{1}{x^2}+\dfrac{1}{y^2}+\dfrac{1}{z^2}}\)
\(=\sqrt{\left(\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}\right)^2-2\cdot\left(\dfrac{1}{xy}+\dfrac{1}{yz}+\dfrac{1}{xz}\right)}\)
\(=\sqrt{\left(\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}\right)^2-2\cdot\dfrac{x+y+z}{xyz}}\)
\(=\sqrt{\left(\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}\right)^2}\)
\(=\left|\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}\right|\)
ND
1
DT
Đỗ Thanh Hải
CTVVIP
13 tháng 9 2021
1 Who have the custom of making....?
2 What do people in the Central Highlands believe?
3 What would they do if the dead weren't buried in beautiful graves
4 What do they make funeral houses and cutting wooden statues for?
5 How many tools do people in the central highlands use to make statues
6 What are the topics for funeral statues aken from?
a.\(C\%_{KCl}=\dfrac{20}{600}.100=3,33\%\)
b.2,5kg = 2500g
\(C\%_{Al_2\left(SO_4\right)_3}=\dfrac{34,2}{2500}.100=1,368\%\)
`(a): C%_[KCl] = 20 / 600 . 100 ~~ 3,33 %`
________________________________________
`(b):` Đổi `2,5 kg = 2500 g`
`C%_[Al_2 (SO_4)_3] = [ 34,2 ] / 2500 . 100 = 1,368%`