Ai giúp mình với đi ạ 

exs1

1 don't have to

3 mustn't

7  don't have to

exs2

3 might

4 can't

7 might be

còn nữa ...

mgu

1) Vì x=25 thỏa mãn ĐKXĐ nên Thay x=25 vào biểu thức \(A=\dfrac{\sqrt{x}-2}{x+1}\), ta được:

\(A=\dfrac{\sqrt{25}-2}{25+1}=\dfrac{5-2}{25+1}=\dfrac{3}{26}\)

Vậy: Khi x=25 thì \(A=\dfrac{3}{26}\)

2) Ta có: \(B=\dfrac{\sqrt{x}-3}{\sqrt{x}+1}+\dfrac{2x+8\sqrt{x}-6}{x-\sqrt{x}-2}\)

\(=\dfrac{\left(\sqrt{x}-3\right)\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}+\dfrac{2x+8\sqrt{x}-6}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{x-5\sqrt{x}+6+2x+8\sqrt{x}-6}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3x+3\sqrt{x}}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3\sqrt{x}\left(\sqrt{x}+1\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}\)

\(=\dfrac{3\sqrt{x}}{\sqrt{x}-2}\)

câu 3 chứ

a/ HĐT của đoạn mạch:

Ta có: \(U_{AB}=U_1=R_1.I_1=10.1,2=12\left(V\right)\)

b/ CĐDĐ I₂ là:

Ta có: \(I=I_1+I_2\Leftrightarrow I_2=I-I_1=1,8-1,2=0,6\left(A\right)\)

  Điện trở R₂ là:

 \(R_2=\dfrac{U_2}{I_2}=\dfrac{U_1}{I_2}=\dfrac{12}{0,6}=20\left(\Omega\right)\)

Tham khảo:
I do not play many kinds of sports, but I love to go swimming. Swimming is just my hobby, but sometimes I also participate in some competitions at my school and local area. When I first went to the pool, I just simply wanted to know how to survive when we felt into water, and it gradually became my favorite thing to do in free time. It took me two weeks to finally floating and swimming for a couple of meters. Before that, I had to struggle very hard and drink a lot of water. However, once I could learn the right technique, swimming became so easy and relaxing. Besides the chance to survive, it can also have many other positive impacts on me. After swimming for about two years, I became taller than most of my friends at the same age. Besides, my muscles also be stronger and tougher, and now I can swim or run slowly for a couple of kilometers without being too tired. I usually go to the pool at the weekend, but if there is an upcoming competition, I have to practice for almost everyday. My strong point is swimming in short distance because I can swim pretty fast. Therefore, I usually sign up in the 100m and 200m categories. The time result is the one to determine the winner, and we need to train to become faster and faster after each competition. I have two bronze medals, two silver medals and one gold medals; my mother keeps them carefully in a glass cabinet, and I can say that they are my biggest pride. Swimming is not simply an activity, but it is both a surviving skill and a supporter for our health. I see many benefits of it, so I will always keep on swimming.
 

a: Xét ΔABC có

E là trung điểm của AB

D là trung điểm của AC

Do đó: ED là đường trung bình của ΔABC

Suy ra: ED//BC và \(ED=\dfrac{BC}{2}\left(1\right)\)

Xét ΔGBC có

M là trung điểm của GB

N là trung điểm của GC

Do đó: MN là đường trung bình của ΔGBC

Suy ra: MN//BC và \(MN=\dfrac{BC}{2}\left(2\right)\)

Từ (1), (2) suy ra ED//MN và ED=MN

Xét tứ giác EMND có 

ED//MN

ED=MN

Do đó: EMND là hình bình hành

b: Ta có: \(ED=\dfrac{BC}{2}\)

mà \(MN=\dfrac{BC}{2}\)

nên ED=MN