`a,` `\Delta ABE ~ \Delta ACF(g-g)` vì đây là hai `\Delta` vuông và có một `\hat(A)` nhọn là góc chung.

`=>(AB)/(AC)=(AE)/(AF)=>AB.AF=AC.AE`

`b,` Có `\Delta AEF ~ \Delta ACB(c-g-c)` do có góc `A` chung và tỉ số `(AB)/(AC)=(AE)/(AF)`
`=>hat(AFE)=hat(ACB)`

Making models involves the creative process of constructing simplified representations or simulations of real-world objects, systems, or phenomena. Whether it's a scale model of a building, a mathematical model of a biological process, or a computer-generated 3D model for a video game, the art of making models requires a combination of imagination, technical skills, and attention to detail. Models serve various purposes, including visualization, experimentation, prediction, and problem-solving. They enable us to explore complex concepts, analyze data, and communicate ideas effectively. From architects and scientists to artists and engineers, the process of making models bridges the gap between imagination and reality, allowing us to better understand and interact with the world around us.

`1999^10+1<1999^10 .1999`
Là hiển nhiên

1. Last year they weren't good students
2. 4 days ago, there was a lot of homework in my book.
3. They are workers.
4. What do they do?

**Bài 1:**

1. good
2. good
3. well
4. good
5. well
6. well
7. well
8. good
9. well
10. good

**Bài 2:**

1. well-behaved
2. well-known
3. well-kept
4. well-written
5. well-informed
6. well-dressed
7. well-paid

**Bài 3:**

1. **I'm tried because I've been working hard.** (Wrong. The correct word is "tired".)
2. I tried hard to remember her name, but I couldn't. (Correct.)
3. This coat is practically unused. I've hardly worn it. (Correct.)
4. Judy is a good tennis player. She hits the ball hard. (Wrong. The correct word is "hardly".)
5. Don't walk so fast! I can't keep up with you. (Correct.)
6. I had plenty of time, so I was walking slow. (Wrong. The correct word is "slowly".)

**Bài 4:**

1. Scott and Tracy have only met once before. They hardly know each other.
2. You're speaking very quickly. I can hardly hear you.
3. I'm very tired this morning. I hardly slept last night.
4. We were so shocked when we heard the news, we could hardly say anything.
5. Kate was very quiet this evening. She hardly said a word.
6. You look the same now as you looked 15 years ago. You haven't changed a bit.
7. I met Dave a few days ago. I hadn't seen him for a long time and he looks very different now. I hardly recognized him.

**Bài 5:**

1. I'll have to go shopping. There's hardly anything to eat.
2. It was a very warm day and there was hardly any wind.
3. "Do you know much about computers?" "No, hardly anything."
4. The hotel was almost empty. There was hardly anybody staying there.
5. I listen to the radio quite often, but I hardly ever watch television.
6. Our new boss is not very popular. Hardly anyone likes her.
7. It was very crowded in the room. There was hardly any room to sit.
8. We used to be good friends, but we hardly ever see each other now.
9. It was nice driving this morning. There was hardly any traffic.
10. I hate this town. There's nothing to do and nowhere to go.

`=8x^3-1-8x^3-8`

`=-9`

HĐT số 7: `(A-B)(A^2+AB+B^2)=A^3-B^3`

`a,=(x+4)^2`

`b,=(3x-4)^2`

`c,=(x-3/2)^2`

`d,=(2xy^2-y)^2`

`e,=(x-2y-2)^2`

`f,=x^2-6xy+9y^2=(x-3y)^2`

HĐT số 1,2: `A^2+-2AB+B^2=(A-B)^2`

`C(y)=(y+2)^2+(y-5)^2=y^2+4y+4+y^2-10y+25=2y^2-6y+29=2(x^2-3x+9/4)+49/2=2(x-3/2)^2+49/2>=49/2`

Dấu "=" xảy ra `<=>x=3/2`

Vậy `C(y)_(min)=49/2<=>x=3/2`

tks

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