Kh MN's Profile

Lập bảng :

                      KLCV(cây)            NS(cây/ngày)            TG(ngày)

Dự kiến               600                     600/x                         x

Thực tế               600                    600/x-1                      x-1

                  Pt : 

Sau đó bạn gọi các đại lượng trên bảng rồi giải pt ra x = 5 nhé

Xét ABC vuông tại A, đường cao AH có :

      AB² = BH . BC ( hệ thức lượng trong tam giác vuông)

     144  = BC.(BC - CH)

     144  = BC. (BC - 12,8)

     144  = BC² - 12,8.BC

     BC² -12,8.BC-144 = 0

   BC = 20 (cm)

 Có : AB² + AC² = BC² ( Định lý Pytago)

       12² + AC² = 20²

             AC = 16 (cm)

 Có : BH + CH = BC

      BH + 12,8 = 20

            BH = 7,2 (cm)

Có : AH² = BH.HC ( hệ thức lượng trong tam giác vuông)

       AH² = 7,2 . 12,8 = 92,16

   AH  = 9,6 (cm)

a) (4x -2)(3x -9) = 0

 TH1: => 4x - 2= 0            TH2: => 3x-9 = 0

         => 4x     = 2                    => 3x    = 9

         => x       = 1/2                 => x      = 3

Vậy phương trình co 2 no  x=1/2 và x=3

b) 3x² + 7x =0

<=> x ( 3x +7 ) = 0

TH1 => x = 0                            TH2 => 3x+7 = 0

                                                        =>  x     = -7

     Vậy phương trình có 2 no  x= 0 và x=7                                                  

c) ( 2x-1 )( 5x+2 )= ( 2x-1 )( 3x-7 )

<=> (2x-1)(5x+2) - (2x-1)(3x-7) = 0

<=> (2x-1)( 5x+2 -3x+7) = 0

<=> (2x-1)( 2x +9) = 0

TH1 => 2x - 1 = 0                    TH2 => 2x + 9 = 0

       => 2x      = 1                           => 2x       = -9

       => x        = 1/2                        => x         = -9/2

Vậy phương trình có 2 n_o x = 1/2 và x = - 9/2

d) 16x³ -9x = 0

<=> x (16x² -9) = 0

<=> x (4x-3)(4x+3) = 0

TH1 => x = 0          TH2 => 4x-3 = 0             TH3: => 4x+3 = 0                                           => 4x    = 3                     => 4x     = - 3 

                                     => x      =  3/4                 => x      =  -3/4

Vậy phương trình có 3 no x=0, x= 3/4, x=-3/4

e) x³ -3x² - 4x +12 =0

<=> x²( x-3) - 4(x-3) =0

<=> (x-3)( x² -4) =0

<=> (x-3)(x-2)(x+2) =0

TH1 => x-3= 0              TH2 => x-2 =0             TH3 => x+2 =0

       => x   = 3                     => x    = 2                   =>  x  = - 2 

Vậy phương trình có 3 no x = 3, x = 2 và x  = -2

f) 3x² -5x +8 = 0

<=> 3x² +3x - 8x +8 =0

<=> 3x( x+ 1) - 8( x+1) =0

<=> ( x+1)(3x-8) = 0

TH1 => x+1 =0          TH2 => 3x+8 = 0

       => x     = -1               =>  x      = -8/3

Vậy phương trình có 2 no x =-1 và x = -8/3

Bai 1 :

1. C, Before                        6. B, as soon as                      11. C, since

2. A, in case                        7. A, until                              12. A, so that

3. B, although                      8. C, unless                           13. C, Once

4. C, while                           9. C, even though                  14. C, whereas

5. A, as                               10. A, as if                            15. A, when

2. Because of being old, she can't work hard.

3. Because of the hard life, he left school.

4. It's time you cleaned your room. 

5. We started leaning English 4 years ago.

V. 

1. Many rivers and lakes are poisoned because factories produce waste and puor it into rivers and lakes.

2. The environment is polluted makes the birds leave their habits and plants die.

3. Plastic bag are major source of waste, so we should not throw plastic bags everywhere.

4. The food is contaminated results in people's health is poor.

5. The air people breath gets polluted due to the fact that factories release fumes.

6. I couldn't sleep because there was a loud noise next to my door last night.

7. The tsunami happened made many people in this area become homeless.

8. The acid rain happened last month since many plants and trees died.

 Đây nha

1) C

2) A

3) C

4) B

5) B

1. Our teachers have explanied the English grammar

=> The English grammar are explaned by our teachers.

2. Some drunk drivers caused the acceident in this city.

=> The accident in this city were caued by some drunk drivers.

3. Tom will visti his parents next month.

=> Tom's parent will be visit by Tom next month.

4. The manager didn't phone the secretary this morning.

=> The secretary weren't phoned by the manager this morning.

5. I won't hang these old pictures in the livign room.

=> These old pictures won't be hung by me in the living room.

6. The German didn't build this factory during the Second World War.

=> This factory weren't built by the German during the Second World War.

7. The students have discussed the pollion problems since last week.

=>The pollution problems have been discussed by the students since last week.

8. Some people will interview the new president on TV.

=> The new president will be interviewed by some people on TV.

9. He has broken his nose in a football match.

=> His nose have been broken in a football match.

10.The waiter brings me this dish.

=> This dish is brought by the waiter to me.

11. Our friends send these postcards to us.

=> These postcards are send by our friends to us.

12. Their grandmother told them this story when they visited her last week.

=> They were told this story by their grandmother when they visited her last week.

13. Tim ordered this train ticket for his mother.

=> This train ticket was ordered by Tim for his mother.

14. You didn't show me the special cameras.

=> I weren't showed the special cameras by you.

15. She showed her ticket to the airline agent.

=> Her ticket was showed to the airline agent by her.

 

 

I.   1. a

     2. d

     3. c

     4. b

     5. a

II.  1. a            6. c

     2. a             7. a

     3. c             8. a

     4. d             9. b

     5. d             10. d

III.  1.b reads -> reading

       2.b sing -> sings

       3.b spending-> spend

       4.a plays -> play

       5.c which -> that 

IV. 1. is taking

     2. was having

     3. was ringing

     4. playing

     5. reading

     6. to lock

     7. going

     8. wrote

     9. didn't receive

     10. don't save

1. He is said to work 16 hours a day.

Đây bạn

 

Theo mình đáp án là C.Mĩ  nhé 

Vì thời kì này kinh tế Mĩ rất phát triển.