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cái bóng của con voi

Lời giải:
a. $x^2-4x-5=0$
$\Leftrightarrow (x+1)(x-5)=0$

$\Leftrightarrow x+1=0$ hoặc $x-5=0$

$\Leftrightarrow x=-1$ hoặc $x=5$

b. 

$5x^2-9x-2=0$
$\Leftrightarrow (x-2)(5x+1)=0$

$\Leftrightarrow x-2=0$ hoặc $5x+1=0$

$\Leftrightarrow x=2$ hoặc $x=\frac{-1}{5}$

c.

$(x^2+1)-5(x^2+1)+6=0$

$\Leftrightarrow a^2-5a+6=0$ (đặt $x^2+1=a$)

$\Leftrightarrow (a-2)(a-3)=0$

$\Leftrightarrow a-2=0$ hoặc $a-3=0$

$\Leftrightarrow x^2-1=0$ hoặc $x^2-2=0$

$\Leftrightarrow (x-1)(x+1)=0$ hoặc $(x-\sqrt{2})(x+\sqrt{2})=0$

$\Leftrightarrow x\in\left\{\pm 1; \pm \sqrt{2}\right\}$

d.

$(x^2+6x)-2(x+3)^2-17=0$

$\Leftrightarrow (x^2+6x+9)-2(x+3)^2-26=0$

$\Leftrightarrow (x+3)^2-2(x+3)^2-26=0$
$\Leftrightarrow -(x+3)^2-26=0$

$\Leftrightarrow (x+3)^2=-26<0$ (vô lý)

Do đó không tồn tại $x$ thỏa mãn.

\(\Rightarrow2x-5=x\)

\(\Rightarrow x+x-5=x\)

\(\Rightarrow x=x+5-x\) (chuyển vế)

\(\Rightarrow x=5\)

Lời giải:

$(2x-5)^8=x^8$

$\Rightarrow 2x-5=x$ hoặc $2x-5=-x$
$\Rightarrow x=5$ hoặc $x=\frac{5}{3}$

Today, I will talk about the similarities and the differences between Landmark 72 and Lotte tower. Lotte tower is shorter than Landmark 72 ( Lotte tower only has 65 floor but Landmark has 72 floor) I special like Lotte because it didn’t has only flat. It also has cinema, hotel, shopping centre too. I still think that Lotte is better than Landmark because the Lotte Tower also has a modern architecture that make me very surprising when i go to explore in Hanoi .But landmark is also interesting. I didn’t go to landmark anytime before but i think Landmark is the vietnam’s second interesting skyscraper. In the highest floor of Landmark ( floor 81) we can see the most beautiful landscape of entire capital city of Vietnam ( Hanoi).

Những đoạn in đậm trên cho thấy câu sai ngữ pháp, sai khá nhiều, mình sửa lại như sau:

Today, I will talk about the similarities and differences between Landmark 72 and Lotte Tower. Lotte Tower is shorter than Landmark 72 ( Lotte Tower only has 65 floors but Landmark has 72 floors) I special like Lotte because it doesn’t have only flats. It also has a cinema, hotel, and shopping center. I still think that Lotte is better than Landmark because the Lotte Tower also has a modern architecture that makes me very surprised when I go to explore in Hanoi . But the landmark is also interesting. I didn’t go to Landmark anytime before but I think Landmark is Vietnam’s second most interesting skyscraper. On the highest floor of Landmark ( floor 81), we can see the most beautiful landscape of the entire capital city of Vietnam ( Hanoi).

  2.[( 7 - 3³: 3²):2² + 99] - 100

= 2.[(7 - 3) : 4 + 99] - 100

= 2. [1 + 99] - 100

= 200 - 100

= 100

= 0

*¹ ϵ {1; 2; 3; 4;...9} 

*^{2 =} 0

5[(85 - 35 : 7) : 8 + 90] - 50

= 5[(85 - 5) : 8 + 90] -  50

= 5.[ 80 : 8 + 90] - 50

= 5.[ 10 + 90 ] - 50

= 5. 100 - 50

= 500 - 50

= 450

5[(85 - 35 : 7) : 8 + 90] - 50

= 5[(85 - 5) : 8 + 90] -  50

= 5.[ 80 : 8 + 90] - 50

= 5.[ 10 + 90 ] - 50

= 5. 100 - 50

= 500 - 50

= 450

Bài này cô làm cho em rồi mà sao em hỏi nhiều vậy

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