7 - x - 1 = 3x + 14

=>4x + 15 = 7

=>4x = -8

=> x = -8 : 4 = -2

7-(x+1)=3x+14

7-(x+1)-14=3x

-7-(x+1)=3x

-7=3x+x+1

-7-1=4x

-8=4x

x=-8/4=-2

=> 7 - x - 1 = 3*x + 14                                                                                                                                            => 6 - x = 3*x + 14                                                                                                                                                => 6 - x - 14 = 3*x                                                                                                                                                  => -8 - x = 3*x                                                                                                                                                        => -8 = 3*x + x = 4*x                                                                                                                                             => x = -8 : 4 = -2

-15+15-17+17+19-18

=0+0+19-18

=0+0+1

=1

=(15-15)+(17-17)+(19-18)

=1 nhé bạn

-15 - 17 + 19 + 15 - 18 + 17 

= ( -15 + 15 ) + ( -17 + 17 ) + ( 19 - 18 )

= 0 + 0 + 1

= 1

a)Công suất hao phí:

\(P_{hp}=\dfrac{P^2\cdot R}{U^2}=I^2\cdot R=100^2\cdot0,2\cdot100=200000W\)

b)Muốn giảm \(P_{hp}\) đi 4 lần thì phải tăng \(U^2=4\Leftrightarrow U=2\) lần vì \(P_{hp}\) tỉ lệ nghịch với bình phương U.

50 kW = 50,000W

4500kJ = 4 500 000 J

Thời gian chuyển động là

\(P=\dfrac{A}{t}\Rightarrow t=\dfrac{A}{P}=\dfrac{4,500,000}{50,000}=90\left(s\right)\) 

Lực kéo đầu tàu là

\(F=\dfrac{P}{v}=\dfrac{50,000}{10}=5000\left(N\right)\)

25 What are you going to do this week?

26 We might go on holiday to the moon in the future

27 There will be a robot in my house

28 The room is very large

25.What are you going to do this week?

26.We might go on holiday to the moon in the future.

27.There will be have robot in my house.

28.The room is large

Chúc bạn học tốt✔✔

1 D

2 A

3 B

II

1 B

2 A

III

1 N

2 D

3 D

4 C

5 A

6 C

7 D

8 A

9 B

10 A

IV

1 has been

2 invited

3 came - was cooking

4 to buy

Part B

1 C

2 D

3 B

4 C

5 C

II

1 It is a day that is meant to raise awareness and appreciation about the Earth's natural environment

2 In 1970

3 Yes, it did

4 C

5 There are more than one hundred and seventy five countries

Part C

1 Despite working hard, he can't support his large family

2 If you don't study harder, you will fail the final exam

3 My brother said that he wanted to go on holiday the day after

4 Most buildings in the city have been destroyed by the earthquake

5 We haven't seen her for 2 months

\(4Al + 3O_2 \xrightarrow{t^o} 2Al_2O_3\\ 2Al + 3Cl_2 \xrightarrow{t^o} 2AlCl_3\\ Al_2O_3 + 6HCl \to 2AlCl_3 + 3H_2O\\ Al_2O_3 + 3H_2SO_4 \to Al_2(SO_4)_3 + 3H_2O\\ AlCl_3 + 3AgNO_3 \to 3AgCl + Al(NO_3)_3\\ Al_2(SO_4)_3 + 3Ba(NO_3)_2 \to Al(NO_3)_2 + 3BaSO_4\\ Al_2(SO_4)_3 + 6KOH \to 2Al(OH)_3 + 3K_2SO_4\\ Al(NO_3)_3 + 3KOH \to Al(OH)_3 + 3KNO_3\\ Al(OH)_3 + NaOH \to NaAlO_2 + 2H_2O\\ 2Al(OH)_3 \xrightarrow{t^o} Al_2O_3 + 3H_2O\)

4Al + 3O2 -> 2Al2O3

Al2O3 + 6HCl -> 2AlCl3 + 3H2O

2Al + 6HCl -> 2AlCl3 + 3H2

Al2O3 + 3H2SO4 -> Al2(SO4)3 + 3H2O

AlCl3 + 3AgNO3 -> Al(NO3)3 + 3AgCl

Al2(SO4)3 + 3Ba(NO3)2 -> 2Al(NO3)3 + 3BaSO4

Al(NO3)3 + 3NaOHvừa đủ -> Al(OH)3 + 3NaNO3

Al2(SO4)3 + 3Ba(OH)2vừa đủ -> 2Al(OH)3 + 3BaSO4

Al(OH)3 + NaOH -> NaAlO2 + 2H2O

2Al(OH)3 -> Al2O3 + 3H2O

Al2O3 + 2NaOH -> 2NaAlO2 + H2O
 

\(4Al+3O_2\underrightarrow{^{t^0}}2Al_2O_3\)

\(2Al+6HCl\rightarrow2AlCl_3+3H_2\)

\(Al_2O_3+6HCl\rightarrow2AlCl_3+3H_2O\)

\(Al_2O_3+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\)

\(AlCl_3+3AgNO_3\rightarrow Al\left(NO_3\right)_3+3AgCl\)

\(Al_2\left(SO_4\right)_3+3Ba\left(NO_3\right)_2\rightarrow2Al\left(NO_3\right)_3+3BaSO_4\)

\(Al_2\left(SO_4\right)_3+6NaOH\rightarrow2Al\left(OH\right)_3+2Na_2SO_4\)

\(Al\left(NO_3\right)_3+3NaOH\rightarrow Al\left(OH\right)_3+3NaNO_3\)

\(NaOH+Al\left(OH\right)_3\rightarrow NaAlO_2+2H_2O\)

\(2Al\left(OH\right)_3\underrightarrow{^{t^0}}Al_2O_3+3H_2O\)

\(2NaOH+Al_2O_3\rightarrow2NaAlO_2+H_2O\)

Uh mình chỉ giúp được câu a

\(x^2-5x+3=0\)

\(\Delta=b^2-4ac\)

\(=\left(-5\right)^2-4.1.3\)

\(=25-12=13>0\)

\(x1=\dfrac{b+\sqrt{\Delta}}{2a}=\dfrac{5+\sqrt{13}}{2}\)

\(x2=\dfrac{b-\sqrt{\Delta}}{2a}=\dfrac{5-\sqrt{13}}{2}\)

là \(\frac{52}{3}\)nhé

hình như đề bài sai bn ơi

Không sai đâu ạk

1)80-63x-7x-4x=10

80-[(63-7-4)x)]=10

80-52x=10

52x=80-10

52x=70

x=70/52

x=35/26