mọi ngi cứu e với
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e, \(x\left(x+1\right)\) = 2 + 4 + 6 + 8 + 10 +...+ 2500
Đặt A = 2 + 4 + 6 + 8 + 10 +...+ 2500
Dãy số trên là dãy số cách đều với khoảng cách là: 4 - 2 = 2
Số số hạng của dãy số trên là: (2500 - 2): 2 + 1 = 1 250 (số)
Tổng A là: A = (2500 + 2) \(\times\) 1250 : 2 = 1563750
\(x\left(x+1\right)\) = 1250 \(\times\) 1251
vậy \(x\) = 1250
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\(n_{Al}=\dfrac{5,4}{27}=0,2\left(mol\right)\\a, 2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\\ n_{H_2}=n_{H_2SO_4}=\dfrac{3}{2}.0,2=0,3\left(mol\right)\\ b,V_{H_2\left(đktc\right)}=0,3.22,4=6,72\left(l\right)\\ c,n_{Al_2\left(SO_4\right)_3}=\dfrac{1}{2}.0,2=0,1\left(mol\right)\\ m_{Al_2\left(SO_4\right)_3}=0,1.342=34,2\left(g\right)\\ d,C\%_{ddH_2SO_4}=\dfrac{0,3.98}{200}.100\%=14,7\%\\ e,m_{ddmuoi}=5,4+200-0,3.2=204,8\left(g\right)\\ C\%_{ddAl_2\left(SO_4\right)_3}=\dfrac{34,2}{204,8}.100\%\approx16,699\%\)
\(a)2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\\ b)n_{Al}=\dfrac{5,4}{27}=0,2mol\\ 2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\)
\(0,2-\rightarrow0,3--\rightarrow0,1--\rightarrow0,3\)
\(m_{H_2}=0,3.2=0,6g\\ c)m_{Al_2\left(SO_4\right)_3}=0,1.342=34,2g\\ d)C_{\%H_2SO_4}=\dfrac{0,3.98}{200}\cdot100=14,7\%\\ e)C_{\%Al_2\left(SO_4\right)_3}=\dfrac{34,2}{5,4+200-0,6}\cdot100=16,7\%\)
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a) tỉ số truyên i
\(i=\dfrac{80}{40}=2\)
b)số vòng quay của đĩa xích
\(\dfrac{80}{50}=\dfrac{8}{5}=1,6\left(vòng\right)\)
I/
2. visited
3. am
4. will lend
5. would get
6. came
7. will see
8. gets
9. would tell
10. will wash
11. won't see
12. ate
13. have
14. got
15. will buy
II/
2. tell/will help
3. wouldn't marry/was
4. didn't fall/ wouldn't break
5. sings/will join
6. would go/were
7. was/would go
8. saw/would say
9. would go/ wasn't
10. had/would give
11. played/would won
12. were/would accept
13. would have/didn't rain
14. went/would see
15. were/would help
16. knew/would go
18. doesn't lend/won't be