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a: \(=\left(2a^2-3a^2-4a^2\right)+\left(-0.5a-2.5a+3a\right)+\left(5-4+7\right)=-5a^2+8\)

b: \(=\left(a^3-a^3\right)+\left(-2a^2-3a^2+4a^2\right)+\left(a+a-a\right)+\left(-5+4\right)=-a^2+a-1\)

c: \(=-b^4+3b^2-3b-1-b^3+1-3b^2+b^4-5+4b^3+5\)

\(=3b^3-3b\)

1:I’m sorry if I’m spoiling but my favorite movie moment is the final battle between the Avengers and Thanos army in the Marvel movie: The Avenger: Endgame. This is the latest installment of The Marvel Cinematic Universe. It concludes a whole epic journey of lots of beloved characters in the movie.

The main plot line of the Avengers: Endgame is the fight between Thanos, a powerful alien , and the Earth protectors, the Avengers who consists of famous superheroes like Iron Man, Captain America, Black Widow, Hawkeye, the Hulk to name a few. Avengers: Endgame is a celebration of the characters , creatures and weapons that have been introduced throughout the Marvel cinematic Universe.

I have three words to describe my favorite moment in the movie: epic , suspenseful and moving. Every superheroes in the previous movies all showed up to fight against the mighty army of the evil Thanos. Thecinematography was amazingly made, the movie soundtrack and the action sequences gave me goosebumps and the final moment when Iron Man defeated Thanos was just too emotional .

The battle was my favorite moment of the entire movie because it’s the final fight that concludes the whole roller coaster ride from previous Marvel movies. As a hardcore fan , everything about Endgame was amazing and satisfying to watch. I will definitely watch it again even though it’s 3 hours long.

2:Saving energy means decreasing the amount of energy used while achieving a similar outcome of end use. Using less energy has lots of benefits – you can save money and help the environment. Generating energy requires precious natural resources, for instance coal, oil or gas. Therefore, using less energy helps us to preserve these resources and make them last longer in the future. There are some tips to save power which I think are very easy to apply. Firstly, change your travel behaviors, think more in terms of public transportation, if possible, walk or ride your bicycle instead of taking the car. Secondly, we should use choose products that come with lightweight packaging and turn off lights and appliances when you are not using them, use energy-saving light bulbs. Thirdly, we should reuse plastic bags for shopping and storage. Finally, we should use a microwave instead of a stove to reheat food and use rechargeable batteries instead of disposable batteries. It's an easy way to save our planet.

Câu 1: 

a,MCD: R1//R2

\(R_{12}=\dfrac{R_1R_2}{R_1+R_2}=\dfrac{30\cdot20}{30+20}=12\left(\Omega\right)\)

b, MCD: R3nt(R1//R2)

\(R_{tđ}=R_3+R_{12}=30+12=42\left(\Omega\right)\)

Câu 2

a Điện trở và cường độ dòng điện tối đa mà biến trở đó có thể có

b,\(S=\dfrac{l\cdot\rho}{R}=\dfrac{100\cdot1,1\cdot10^{-6}}{200}=5,5\cdot10^{-7}\)

\(R=\sqrt{\dfrac{S}{\pi}}=\sqrt{\dfrac{5,5\cdot10^{-7}}{\pi}}=4,18\cdot10^{-4}\left(m\right)=0,418\left(mm\right)\)

\(x^3+2x^2\left(4y-1\right)-4xy^2-9y^3-f\left(x\right)=-5x^3+8x^2y-4xy^2-9y^3\\ \Rightarrow\left(x^3+8x^2y+2x^2-4xy^2-9y^3\right)-f\left(x\right)=-5x^3+8x^2y-4xy^2-9y^3\\ \Rightarrow f\left(x\right)=x^3+8x^2y+2x^2-4xy^2-9y^3+5x^3-8x^2y+4xy^2+9y^3\\ \Rightarrow f\left(x\right)=6x^3+2x^2\)

1.B 2.C nha

B

C

1.B

2.C

 => 1 đvC = \(\frac{1,996.10^{-23}}{12}\) ≈ 1,66.10^-24 (g).

1 đơn vị cacbon hay ghi tắt là 1đ.v.c bằng:

(1,9926.10^-23)/12      (g)

1Cacbon= 1,6605.10^-24 g

Bài 2 đâu hả bn

@Mina

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