\(\left\{{}\begin{matrix}P=U.I\Rightarrow I=\dfrac{P}{U}=\dfrac{100}{220}=\dfrac{5}{11}\left(A\right)\\R=\dfrac{U}{I}=\dfrac{220}{\dfrac{5}{11}}=484\left(\Omega\right)\end{matrix}\right.\)

\(R_Đ=\dfrac{U_Đ^2}{P_Đ}=\dfrac{220^2}{100}=484\Omega\)

a)Cường độ dòng điện:

   \(I_m=\dfrac{U_m}{R}=\dfrac{220}{484}=\dfrac{5}{11}A\)

b)Cường độ dòng điện khi đặt 1 hđt 200V vào hai đầu đèn:

    \(I'=\dfrac{200}{484}=\dfrac{50}{121}A\)

   Điện năng đèn tiêu thụ trong 10' :

    \(A=UIt=200\cdot\dfrac{50}{121}\cdot10\cdot60=49586,8J\)

II

1 C

2 B

3 C

4 D

5 A

6 A

7 D

8 C

III

1 is getting

2 is - is visited

3 selling

4 were you doing - phoned

IV

1 This road isn't used very often

2 A lot of trees will be grown in the park

3 The living-room is being painted light blue

4 Many different paper products have been developed

5 We were asked many difficult questions by the examier

V

1 It's is coffee "black" without cream or sugar

2 They are China, Japan and other Oriental countries

3 They drink tea with sugar

4 Yes, it is

VI

1 drive => driving

2 That => the

3 meets => has met

4 getting => to get

Đề 2

Bài 1

1C

2D

3D

4C

Bài 2

1 C

2 A

3 C

4 B

5D

6 D

7 C

8 D

9 B

10 A

Bài 3 

1 is going to rain

2 haven't invited

3 is getting

4 saw

Thay m=2 vào HPT ta có: 

\(\left\{{}\begin{matrix}2x+y=1\\x+2y=1\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}4x+2y=2\\x+2y=1\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}4x+2y=2\\3x=1\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}x=\dfrac{1}{3}\\y=\dfrac{1}{3}\end{matrix}\right.\)

b) \(\left\{{}\begin{matrix}mx+y=1\\x+my=1\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}y=1-mx\\x+m\left(1-mx\right)=1\left(1\right)\end{matrix}\right.\)

(1) ⇔x+m-m²x=1

⇔x(1-m²)=1-m (2)

TH1: 1-m² = 0

⇔m = +- 1

Thay m=1 vào (2) ta có: 0x=0 (Luôn đúng) ⇒m=1 (chọn)

Thay m=-1 vào (2) ta có: 0x=2 (Vô lí) ⇒m=-1 (loại)

TH2: 1-m² ≠0

⇔m≠ +-1

⇒HPT có nghiệm duy nhất:

x=  \(\dfrac{1-m}{1-m^2}\)

⇒y= \(1-m.\dfrac{1-m}{1-m^2}\)

⇔y=\(\dfrac{1-m}{1-m^2}\)

Dễ thấy x=y nên: 

\(\dfrac{1-m}{1-m^2}>0\)

⇔1-m>0

⇔m<1

Vậy m <1 thì Thỏa mãn yêu cầu đề bài.

a) Thay m=2 vào hệ phương trình, ta được:

\(\left\{{}\begin{matrix}2x+y=1\\x+2y=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x+y=1\\2x+4y=2\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}-3y=-1\\2x+y=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{1}{3}\\2x=1-y=\dfrac{2}{3}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1}{3}\\y=\dfrac{1}{3}\end{matrix}\right.\)

Vậy: Khi m=2 thì hệ phương trình có nghiệm duy nhất là \(\left\{{}\begin{matrix}x=\dfrac{1}{3}\\y=\dfrac{1}{3}\end{matrix}\right.\)

bài ở đâu vậy bạn

em lớp 4:))))

1 We are having a wonderful time at the moment in Sa Pa

2 It is necessary to cool the burn imediately

1.We are having a wonderful time at the moment in Sa Pa

2.It is necessary to cool the burn imediately

V

1 will be watching

2 will make

3 is going to rain

4 will become - won't get

5 will change

6 to call

7 will be lying

8 had come - had been

9 arrived - had been waiting

10 are not

11 pollution

12 were destroyed

13 would do

14 had left - came

15 didn't go - stayed

16 Has - learnt , has learnt

17 Did - wear , didn't wear

18 Does - read , watch

19 would save

20 will have

21 will be being painted

22 smoked

23 came - had left

24 had finished

25 was built

VI

1 

a)

1 T

2 F

3 T

4 T

5 T

6 F

b)

1 It is a device which is used to send multiple messages over a single wire

 2 It is a device which is used to draw the shape of the sound waves

3 It happened in 1876, while bell was at one end of ........

Để hàm bậc 3 có 2 cực trị nằm về 2 phía trục hoành

\(\Leftrightarrow y=0\) có 3 nghiệm pb

\(\Leftrightarrow x^3-\left(2m+1\right)x^2+\left(m+1\right)x+m-1=0\) có 3 nghiệm pb

\(\Leftrightarrow\left(x-1\right)\left(x^2-2mx-m+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x^2-2mx-m+1=0\left(1\right)\end{matrix}\right.\)

Bài toán thỏa mãn khi (1) có 2 nghiệm pb khác 1

\(\Leftrightarrow\left\{{}\begin{matrix}a+b+c=1-2m-m+1\ne0\\\Delta'=m^2+m-1>0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}m\ne\dfrac{2}{3}\\\left[{}\begin{matrix}m< \dfrac{-1-\sqrt{5}}{2}\\m>\dfrac{-1+\sqrt{5}}{2}\end{matrix}\right.\end{matrix}\right.\)

Có 19 số tự nhiên nhỏ hơn 20 thỏa mãn

\(\sqrt{2}\) - \((a)^{2}\)

\(\left(a\right)^2\)

a) 1 = 12/12

b) -5 = -60/12

c) -3/4 = -9/12

d) 0 = 0/12