Cho a; b >0 tm a+2b=< 3. Tìm max của P= \(\sqrt[3]{a+7}+2\sqrt[3]{b+7}\)
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26 tháng 8 2018
a) Từ các đơn chất có thể điều chế hợp chất hoá học.
Pưhh: Fe + Cl2 --> FeCl3
b) Từ hợp chất hoá học có thể điều chế các đơn chất.
Pưhh: H2O ---đp---> H2 + O2
c) Từ hợp chất hoá học này có thể điều chế hợp chất hoá học khác.
Pưhh: Al(OH)3 -to-> Al2O3 + H2O
9 tháng 4 2020
a,\(2KMnO_4\underrightarrow{^{to}}K_2MnO_4+MnO_2+O_2\)
a___________1/2a_______1/2a_______
\(2KClO_3\underrightarrow{^{to}}2KCl+3O_2\)
b___________b______
\(m_{Cr}=m_{K2MnO4}+m_{MnO2}+m_{KCl}\)
\(\Leftrightarrow197.\frac{1}{2}a+87.\frac{1}{2}a+74,5b\)
\(\Rightarrow142a+74,5b\)
b,\(m_{K2MnO4}+m_{MnO2}=m_{KCl}\)
\(\Leftrightarrow142a=74,5b\)
\(\Rightarrow\frac{a}{b}=\frac{74,5}{142}=\frac{149}{284}\)
KL
24 tháng 10 2021
Tìm và chữa lỗi sai
1. Ho Chi Minh City, which named is after President Ho Chi Minh, is quite a young city.
A B C D
2. The child were told to apologize for being rude to his brother.
A(were-> was) B C D
3. When he arrived at the furniture shop, people had been sold the table he wanted.
A B C D
4. The first May Day celebrated in England in 1890.
A B(celebarted-> was celebrated) C D
5. Most of them were build in the nineteenth century and some are very grand.
A B(biuld->built) C D
6. In many universities, English taught to students althoughName=7; HotwordStyle=None; it is not the native language.
A B(taught->is taught) C D
7. Two prisoners were hang this morning by the Taliban.
A B(were hang->were hung) C D
8. Daisy's ring is make of gold.
A B C(is make-> is made) D
9. The literal work “Hamlet” was wrote by William Shakespeare.
A B(was wrote-> was written) C D
10. Chinese is studying by Henry every night.
A B(studying-> studied) C D
11. More people are infecting with HIV this year than they were 5 years ago.
A B (infecting -> infected) C D
12. The meeting was be rearranged shortly before it had been due to take place.
A(was be->was) B C D
13. Every possible effort were made by the orphanage to find the boy’s parents.
A B (were -> was) C D
14. Cheques should only be accept with proof of identity.
A B( be accept -> be accepted) C D
15. Dent station is situated on the Seattle to Carlisle railway line, said be the most scenic in the
A B C(be->to be) D
country.
16. Do not blame me if the tin-opener is break.
A B C D(break-> broken)
17. This class has canceled because too few students had registered before registration closed.
A(canceled-> been canceled) B C D
18. This building will have finished by the end of 2020.
A(will have finished-> will have been finished) B C D
19. A new road is built across this field next six months.
A(is built-> will be built) B C D
20. All his attempts are supporting heartily by his relatives and neighbors
A(are supporting-> are supported) B C D
Chúc bạn học tốt!
22 tháng 12 2019
Bài 1:
\(CTTQ:Al_xO_y\)
Theo QTHT, ta có:
\(x.III=y.II\Leftrightarrow\frac{x}{y}=\frac{II}{III}=\frac{2}{3}\)
=> x=2, y=3
\(CTHH:Al_2O_3\)
\(CTTQ:Zn_xCl_y\)
Theo PTHH, ta có:
\(x.II=y.I\Leftrightarrow\frac{x}{y}=\frac{I}{II}=\frac{1}{2}\)
=> x=1, y=2
\(CTHH:ZnCl_2\)
Câu 6:
\(V_{hh}=n_{hh}.22,4=\left(0,1+0,2\right).22,4=6,72\left(l\right)\)
=> Câu C
KH
31 tháng 7 2019
\(CTPT:Al_xO_y\\ Theo.QTHT\\ \Rightarrow x.III=y.II\Leftrightarrow\frac{x}{y}=\frac{II}{III}=\frac{2}{3}\\ \rightarrow CTHH:Al_2O_3\rightarrow A\)
31 tháng 7 2019
Gọi CTHH là AlxOy
Theo quy tắc hóa trị ta có:
\(x\times III=y\times II\)
\(\Rightarrow\frac{x}{y}=\frac{II}{III}=\frac{2}{3}\)
Vậy CTHH là Al2O3
Chọn A
LT
1 tháng 10 2019
2R+2 H2O--->2ROH+H2
n\(_{H2}=\frac{2,24}{22,4}=0,1\left(mol\right)\)=>m\(_{H2}=0,2\left(g\right)\)
Theo pthh
n\(_R=2n_{H2}=0,2\left(mol\right)\)
M\(_R=\frac{4,6}{0,2}=23\)
=> R là Na
Theo pthh
n\(_{NaOH}=2n_{H2}=0,2\left(mol\right)\)
C% NaOH=\(\frac{0,2.40}{200+4,6-0,2}.100\%=3,91\%\)
NaOH +HCl---->NaCl +H2O
Theo pthh
n\(_{HCl}=n_{NaOH}=0,2\left(mol\right)\)
V\(_{HCl}=\frac{0,2}{2}=0,1\left(l\right)=100ml\)
Chúc bạn học tốt
Ta có \(4\sqrt[3]{a+7}\le\frac{a+7+8+8}{3}=\frac{a+23}{3}\)
\(4\sqrt[3]{b+7}\le\frac{b+23}{3}\)
Từ đó ta có
\(4P=4\sqrt[3]{a+7}+4\sqrt[3]{b+7}+4\sqrt[3]{b+7}\)
\(\le\frac{a+b+b+23×3}{3}=\frac{a+2b+23×3}{3}\le24\)
\(\Rightarrow P\le6\)
Đạt được khi a = b = 1
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