khó nhìn quá :) câu 27 sao câu A,B.C giống nhau z :)

Câu 28: C

Câu 29: B,D

6. C

7. B

8. D

TH1: x>=-5

=>3x+1=x+5

=>2x=4

=>x=2(nhận)

TH2: x<-5

=>-3x-1=x+5

=>-4x=6

=>x=-3/2(loại)

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Cacbon

a) \(Q=\dfrac{\left(x+2\right)^2}{x}\cdot\left(1-\dfrac{x^2}{x+2}\right)-\dfrac{x^2+10x+4}{x}\left(x\ne0;x\ne-2\right)\)

\(Q=\dfrac{\left(x+2\right)^2}{x}\cdot\dfrac{\left(x+2\right)-x^2}{x+2}-\dfrac{x^2+10x+4}{x}\)

\(Q=\dfrac{\left(x+2\right)^2}{x}\cdot\dfrac{-x^2+x+2}{x+2}-\dfrac{x^2+10x+4}{x}\)

\(Q=\dfrac{\left(x+2\right)\left(-x^2+x+2\right)}{x}-\dfrac{x^2+10x+4}{x}\)

\(Q=\dfrac{-x^3+x^2+2x-2x^2+2x+4-x^2-10x-4}{x}\)

\(Q=\dfrac{-x^3-2x^2-6x}{x}\)

\(Q=\dfrac{x\left(-x^2-2x-6\right)}{x}\)

\(Q=-x^2-2x-6\)

b) Ta có:

\(Q=-x^2-2x-6\)

\(Q=-\left(x^2+2x+6\right)\)

\(Q=-\left[\left(x^2+2x+1\right)+5\right]\)

\(Q=-\left(x+1\right)^2-5\)

Mà: \(-\left(x+1\right)^2\le0\forall x\)

\(\Rightarrow Q=-\left(x+1\right)^2-5\le-5\forall x\)

Dấu "=" xảy ra khi:

\(x+1=0\Rightarrow x=-1\)

Vậy: \(Q_{max}=-5\Leftrightarrow x=-1\)

I

1.What type of energy do you use at home?
2.John uses low energy light bulbs to save electricity.
3.Mai can't go to the cinema at present because she is studying for her exam.
4.What book are you currently reading?
5.She is not swimming in the swimming pool at the moment.
6.Scientists are looking for a new energy source to replace coal now

II.

1. Coal is more expensive and more polluting than natural gas.

2. We are looking for cheap and clean and effective sourced of energy..

3.. You should switch off electrical appliances when they aren’t in use.

4. Despite being the most polluting of fossil fuels, coal is still the largest sources of energy worldwide.

5. People will use biogas for fuel in homes and for transport

a.    A= 2+2²+2³+......+2⁶⁰

= 2+ (2²+2³)+(2⁴+2⁵)+......+(2⁵⁸+2⁵⁹)+2⁶⁰

=2+2(2+2²)+2³(2+2²)+......+2⁵⁷(2+2²)+2⁶⁰

=2+(2+2²)(2+2³......+2⁵⁷)+2⁶⁰

=2+ 6(2+2^3+......+2^57)+2⁶⁰ => cả 23 số hạng đều chia hết cho 2 => tổng chia hết cho 2 => a chia hết cho 2

b. A=(2+2^2+2^3+2^4)+(2^5+2^6+2^7+2^8)+.........+(2^57+2^58+2^59+2^60)

=2(1+2+2^2+2^3)+2^5(1+2+2^2+2^3)+......+2^57(1+2+2^2+2^3)

=2.15 +2^5.15+...........+2^57.15 = 15 (2+2^5+...........+2^57) => 15 chia hết cho 3 => A chia hết cho 3

k đúng cho mình nha!!!!

a. Do 2; 2²; 2³; ...; 2⁶⁰ chia hết cho 2

=> A chia hết cho 2 ( đpcm)

b. A = 2 + 2² + 2³ + ... + 2⁶⁰ ( có 60 số; 60 chia hết cho 2)

A = (2 + 2²) + (2³ + 2⁴) + ... + (2⁵⁹ + 2⁶⁰)

A = 2.(1 + 2) + 2³.(1 + 2) + ... + 2⁵⁹.(1 + 2)

A = 2.3 + 2³.3 + ... + 2⁵⁹.3

A = 3.(2 + 2³ + ... + 2⁵⁹) chia hết cho 3

=> A chia hết cho 3 ( đpcm)