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\(a,2xy.3x^2y^4z=6x^3y^5z\)

Hệ số: 6

Biến: \(x^3y^5z\)

Bậc: 9

\(b,\dfrac{1}{2}xy^2t.\dfrac{2}{3}x^2yt^3=\dfrac{1}{3}x^3y^3t^4\)

Hệ số: \(\dfrac{1}{3}\)

Biến: \(x^3y^3t^4\)

Bậc: 10

\(c,\left(\dfrac{1}{2}x^2y^3\right)^3\left(\dfrac{2}{3}xy\right)^2=\dfrac{1}{8}x^6y^9.\dfrac{4}{9}x^2y^2=\dfrac{1}{18}x^8y^{11}\)

Hệ số: \(\dfrac{1}{18}\)

Biến: \(x^8y^{11}\)

Bậc: 19

22

\(\dfrac{-1}{8}\le\dfrac{x}{72}\le\dfrac{-1}{36}\)

\(\dfrac{-9}{72}\le\dfrac{x}{72}\le\dfrac{-2}{72}\)

\(\Rightarrow\) \(x\in\) {\(-9;-8;-7;-6;-5;-4;-3;-2\)}

1T

2F

3C

4A

1Unless Tom studied hard, he wouldn't get good marks

2Tam had a stomachache because he ate a lot last night

a: Xét ΔOAM vuông tại A và ΔOBM vuông tại B có

OM chung

\(\widehat{AOM}=\widehat{BOM}\)

Do đó: ΔOMA=ΔOMB

b: ΔOMA=ΔOMB

=>MA=MB và OA=OB

OA=OB

=>O nằm trên đường trung trực của AB(1)

MA=MB

=>M nằm trên đường trung trực của AB(2)

Từ (1) và (2) suy ra OM là đường trung trực của AB

=>OM\(\perp\)AB

My mother used to work at a restaurant 3 years ago but now she doesn't

He used to be the president of Student Union but now he isn't

There used to be many trees - lined in my hometown but now there is none of them

My husband didn't use to do homework but now he does

Children didn't use to play with high-tech devices at an early age

1. My mom used to work at a restaurant

2. He used to be the president of Student Union

3. There used to be many tree-lined street in my hometown.

4. My husband didn't use to do the housework.

5. The children didn't use to play with high-tech devices.

My mother used to work at  restaurant three years ago.

 He used to be the president of Student Union.

There used to be many tree-lined streets in my hometown.

My husband didn't use to do  housework.

childrent didn't use to play with high-tech devices at an early age.  

a,x=4/5.0,5

x=4/5.1/2

x=2/5

b, thiếu

a) x: 0,5 = 4/5

x= 4/5 x 0,5

x= 2/5

b) đề bị thiếu

a: Xét ΔABC vuông tại A có \(cosB=\dfrac{AB}{BC}=\dfrac{1}{2}\)

nên \(\widehat{B}=60^0\)

b:

ΔABC vuông tại A

=>\(AB^2+AC^2=BC^2\)

=>\(AC^2=6^2-3^2=27\)

=>\(AC=3\sqrt{3}\left(cm\right)\)

Xét ΔBAC có BD là phân giác

nên \(\dfrac{AD}{AB}=\dfrac{CD}{CB}\)

=>\(\dfrac{AD}{3}=\dfrac{CD}{6}\)

=>\(\dfrac{AD}{1}=\dfrac{CD}{2}\)

Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{AD}{1}=\dfrac{CD}{2}=\dfrac{AD+CD}{1+2}=\dfrac{3\sqrt{3}}{3}=\sqrt{3}\)

=>\(\left\{{}\begin{matrix}AD=\sqrt{3}\simeq1,7\left(cm\right)\\CD=2\sqrt{3}\simeq3,5\left(cm\right)\end{matrix}\right.\)

c: ΔABC vuông tại A có AH là đường cao

nên \(AH\cdot BC=AB\cdot AC\)

=>\(AH\cdot6=3\cdot3\sqrt{3}=9\sqrt{3}\)

=>\(AH=\dfrac{3\sqrt{3}}{2}\left(cm\right)\)

d: ΔABC vuông tại A có AH là đường cao

nên \(BA^2=BH\cdot BC\left(1\right)\)

ΔADB vuông tại A có AE là đường cao

nên \(BE\cdot BD=BA^2\left(2\right)\)

Từ (1),(2) suy ra \(BH\cdot BC=BE\cdot BD\)

=>\(\dfrac{BH}{BD}=\dfrac{BE}{BC}\)

Xét ΔBHE và ΔBDC có

BH/BD=BE/BC

\(\widehat{HBE}\) chung

Do đó: ΔBHE đồng dạng với ΔBDC

1You shouldn't spend a lot of time watching TV

2Antarctica is the coldest place in the world

4A car is not as convenient as a bicycle in towns

5Take a first right

1. According/ latest report/ the number/ people/ injured/ typhoon/ nearly/ 150.

=> According to the latest report, the number of people injured in the typhoon was nearly 150.

2. I/ look forward to/ hear/ you/ soon.

=> I am looking forward to hearing from you soon

3. The number/ English speakers/ increase/ recent years.

=> The number of English speakers increased in recent years

4. Tsunamis/ also/ refer/ the public/ tidal waves.

=> Tsunamis are also referred to the public as tidal waves.

5. We/ use/ art/ communicate/ 200 years.

=> We will be using art to communicate in 200 years

1. => According to the latest report, the number of people injured in the typhoon was nearly 150.

2. => I am looking forward to hearing from you soon.

3. => The number of English speakers increased in recent years.

4. => Tsunamis are also referred to the public as tidal waves.

5. => We will be using art to communicate in 200 years.