Câu 2:

\(n_{H_2}=0,2\left(mol\right)\)

\(Mg+H_2SO_4\rightarrow MgSO_4+H_2\)

0,2                                        0,2

\(m_{Mg}=0,2.24=4,8\left(g\right)\)

Câu 1:

a) \(C+O_2\rightarrow CO_2\)

b) \(S+H_2\rightarrow H_2S\)

c) \(NaCl+AgNO_3\rightarrow AgCl\downarrow+NaNO_3\)

d) \(H_2SO_4+Ba\left(OH\right)_2\rightarrow BaSO_4\downarrow+2H_2O\)

Bài 1: 

a) \(\dfrac{-5}{18}+\dfrac{5}{9}-\dfrac{11}{36}=\dfrac{-10}{36}+\dfrac{20}{36}-\dfrac{11}{36}\)\(=\dfrac{-1}{36}\)

b) \(\dfrac{-39}{44}:1\dfrac{2}{11}=\dfrac{-39}{44}:\dfrac{13}{11}=\dfrac{-39}{44}.\dfrac{11}{13}=\dfrac{-3}{4}\)

c) \(\dfrac{-7}{11}.\dfrac{11}{19}+\dfrac{-7}{11}.\dfrac{8}{19}+\dfrac{-4}{11}=\dfrac{-7}{11}.\left(\dfrac{11}{19}+\dfrac{8}{19}\right)+\dfrac{-4}{11}=\dfrac{-7}{11}.1+\dfrac{-4}{11}=-1\)

Bài 2: 

a) \(x+\dfrac{2}{5}=-\dfrac{11}{15}\)

\(\rightarrow x=-\dfrac{11}{15}-\dfrac{2}{5}=-\dfrac{11}{15}-\dfrac{6}{15}=\dfrac{-17}{15}\)

b) \(\left(x-\dfrac{7}{18}\right).\dfrac{18}{29}=-\dfrac{12}{29}\)

\(x-\dfrac{7}{18}=-\dfrac{12}{29}:\dfrac{18}{29}\)

\(x-\dfrac{7}{18}=-\dfrac{12}{29}.\dfrac{29}{18}=-\dfrac{12}{18}\)

\(x=\dfrac{-12}{18}+\dfrac{7}{18}=\dfrac{-5}{18}\)

7A

11B

12D

13A

\(P=\dfrac{x+2+\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)-\left(x+\sqrt{x}+1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}.\dfrac{x+\sqrt{x}+1}{\sqrt{x}-1}\)

\(P=\dfrac{x+2+x-1-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)^2}\)

\(P=\dfrac{x-\sqrt{x}}{\left(\sqrt{x}-1\right)^2}\)

\(P=\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)^2}\)

\(P=\dfrac{\sqrt{x}}{\sqrt{x}-1}\)

\(P< \dfrac{1}{2}\rightarrow\dfrac{\sqrt{x}}{\sqrt{x}-1}< \dfrac{1}{2}\)

\(\dfrac{\sqrt{x}}{\sqrt{x}-1}-\dfrac{\sqrt{x}-1}{2\left(\sqrt{x}-1\right)}< 0\)

\(\dfrac{2\sqrt{x}-\sqrt{x}+1}{2\left(\sqrt{x}-1\right)}< 0\)

\(\dfrac{\sqrt{x}+1}{\sqrt{x}-1}< 0\)

\(\sqrt{x}+1>0\rightarrow\sqrt{x}-1< 0\)

\(\sqrt{x}< 1\)

x<1

Kết hợp lại với đk, ta có : \(0\le x< 1\)

9. D

11. A

13. C

14. A

30. B

2(x+y)+3xy(x+y)+5x²y²(x+y)+4

1. lived

2. has worked

3. Does John

5. Were you putted

6. is studying

7. living

10. came

\(x=9\rightarrow\sqrt{x}=3\)

a) Thay \(\sqrt{x}=3\) vào A ta có :

\(A=\dfrac{3+2}{3-5}=\dfrac{5}{-2}=-\dfrac{5}{2}\)

b) \(B=\dfrac{3}{\sqrt{x}+5}+\dfrac{20-2\sqrt{x}}{x-25}\)

\(B=\dfrac{3\left(\sqrt{x}-5\right)}{\left(\sqrt{x}+5\right)\left(\sqrt{x}-5\right)}+\dfrac{20-2\sqrt{x}}{\left(\sqrt{x}+5\right)\left(\sqrt{x}-5\right)}\)

\(B=\dfrac{3\sqrt{x}-15+20-2\sqrt{x}}{\left(\sqrt{x}+5\right)\left(\sqrt{x}-5\right)}\)

\(B=\dfrac{\sqrt{x}+5}{\left(\sqrt{x}+5\right)\left(\sqrt{x}-5\right)}\)

\(B=\dfrac{1}{\sqrt{x}-5}\) (đpcm)